Fuzzy Recognition of Cricket Batting Strokes based on Sequences of Body and Bat Postures

M G Kelly, K M Curtis* and M P Craven School of Engineering, University of Technology, 237 Old Hope Road, Kingston 6, Jamaica.

*Department of Mathematics and Computer Science University of the West Indies, Mona Campus, Kingston 7, Jamaica.

Abstract Proposed system A mathematical classification of two cricket batting strokes, using fuzzy set theory, is presented. A system is proposed

We aim to design a system to capture the data from the cricketer's body and bat posture whilst playing a stroke.

within this p!per, to capture the motion of a batsmadbatswoman whilst playing a stroke. This is then compared to hown strokes, provided by the classification and feedback is provided which outlines how well the selected stroke was played. This proposed expert system uses motion sensors in the classification process.

Key Words:- Cricket Batting, Fuzzy Sets, Classification,

Introduction Over the years.technology has added new dimensions to sport. The Olympics has benefited greatly. Through motion analysis system the essentials to achieving proper technique in motion for various sporting events has been outlined [I]. Also numerous commercial systems have been developed for the sports of golf, bowling and baseball [2,3,4]. The sport of cricket has also benefited from technology. The most common example of this is the video playback system. The main uses are umpiring and training. Third umpires use such systems to analyse the action of the cricketer and obtain a decision that is consistent with the rules of the game. One such system is used to help in adjudicating in leg before wicket decisions [5 ] . Teams also use these systems for training purposes. They can analyse the motion of the opposing player and determine how best to get the batsman out or how to score

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Cricket is only just starting to embrace the different technologies that can be easily applied to the sport and to date there has not been any significant contribution to the improvement of batting. With the inconsistencies now present in batting and in particular West Indies batting, a batting technique trainer will be significant. Below we suggest such a system and an appropriate classification scheme for batting strokes.'These combined should provide the basis of an efficient cricket badng analysis and training system.

ISBN 0-7803-7856-3/02/$10.00 0 2003 IEEE

We propose to use motion sensors that are currently being used in virtual reality systems [6,7] and other areas [8,9]. Figure 1 shows a block diagram representation of the system. The system consists of sensors, a motion capture interface unit and a computer system.

Sensors Motion Computer cavture svstem

Figure I . Block diagram of proposed system

The sensors will be used to measure the different elements of the classification system. These include electromagnetic position sensors, pressure sensors and pressure mats. The position sensors will indicate the relative positions ofbat, feet, and head position of the batsman. These sensors will be placed, one in the middle at the back of the bat, one on each foot, one on each hand and one on the head. The motion capture interface will provide the means by which the sensors will be interfaced with the computer system. The motion capture system is the Polhemus 3space Fastrak unit. We use electromagnetic sensors rather than cameras because orientation data can be readily obtained from the sensors. The Polhemus Startrak system can be used instead of the Fastrack where the Wires will be replaced by a wireless link. The computer system hosts the software required for the entire system to function. This includes data collection and storage systems along with the programs developed to cater for the classification, analysis and feedback processes.

The entire system measures the elements of the classification (presented via fuzzy sets) and differentiates between the different strokes. This differentiation is made based on the fuzzy rules obtained for each stroke. These rule are developed based on the coachesltrainers description for each stroke. The system will initially be trained using one or a number of experienced batsmen. This training involves the experienced

Proceedings IEEE Southeastcon 2003 140

batsman playing the stroke related to the ball being bowled (For consistency it is suggested that a bowling machine be used). The system then measures the different elements necessary for the stroke classification (See table 3). This will be done on an initial basis for two strokes with the possibility of an expansion to include all the strokes. The system will now use this data to classify, and group the strokes based on the different elements of tabled, 2 and 3. This process will be carried out a number of times with different batsmen to ensure that the system will be able to tolerate the slight variations in the different batting techniques of the batsman.

Based on the analysis, the system provides feedback in the form of an expert system, either to the coach or the player on how efficiently the stroke was played. It comments on the stroke selection compared with the ball being bowled, how well the stroke was executed compared to an experienced player and the player’s natural abilities, that is, showing where the player’s strength lies

Classification of cricket batting strokes Working along with a cricket coach, we have devised a scheme where each stroke is classified based on the positioning of the body, the positioning of the bat and the flight path of the ball. To understand the terms used in this classification refer to figure 2 and figure 3. Figure 2 shows a bud’s eye view of the second half of a cricket pitch (the second 11 yards) with the bowler bowling from left to right to a right-handed batsman (facing the ball with the feet position shown). The pitch is divided into sections representing the different bowling lengths (where the ball iirst makes contact with the ground). Figure 3 shows the reference positions for both body and bat orientation, described from the crease.

The classification is carried out based upon the body position and the ballhat position. These groups are inter-related and their separation is only carried out so as to allow for the easier comparison of limb movements and body positioning. For the body positioning the different groups are; head position, hands position, feet position and the weight distribution on the feet, refer to table 1. Table 2 shows the other half of the classification and this involves; the mode of the stroke being played, the flight path of the ball being bowled, the bat orientation and the area on the bat where the ball makes contact.

These classification criteria were decided upon for the following reasons: Head position: Doing well at batting is largely dependent on

being able to see the ball well. The position of the head determines how well the ball is seen. The head should remain still throughout the execution of the stroke.

Hand positions: This refers to how well the bat is gripped and how the wrists are angled to play each stroke. This largely determines the direction in which the ball will travel after it makes contact with the bat. This area is closely related to the bat orientation. The placing of the feet based on the pitch of the ball is an integral part of the strokes being played.

position. It is important to maintain good balance to be able to play well and the stroke selection will be influenced by the player’s centre of gravity.

Mode of stroke: This describes the stroke in terms of attacking, defensive or semi-attacking.

Ball bowled The decision to play a particular stroke is primarily dependent on the ball being bowled. This refers to the length of the ball (how far away from the stumps it pitches first) and the line of the ball (how closely in line with the stump it pitches). Figure 2

Feet position:

Weight distribution: Clearly this is closely related to the feet

outlines these concepts. . - . Bat orientation: How the bat is orientated is also important in

describing the type of strokes. This orientation refers to the angle at which the bat makes contact with the ball and the plane through which the bat is swung (follow through).

Ball contact on bat: This is important in determining the shot as it gives an idea of the direction of travel of the ball after it makes contact with bat, whether it will travel in the air or along the ground (the trajectory of the ball after bat contact).

For quicker pitches and For slower pitches and slower bowlers

Direction of ball

Frnnt font -\ Crease Figure 2. 7%ejlighl porh for differemf b d s rhar c m be bowled ro a right handed batsman Only Besecond halfof l e crickerpifch isshown from [IO].

Back foot

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toe "=e view from above

m ~ l a n view ofbat

a side view (flat foot)

side vir of bat

f g 3a. representation offoot fig 36. representation of bat

down the pitch

.fn 3d .feet down pitch

at mid wicket

4 r - b - X X --

feet l e e feet nght

'ic. 3 f feet Iefurirht

...................... , , ,

90' 5' fg.3h. forward swing

crease

fect forward front foot

crease

feet backwards 4 A back foot

f ig 3c feet fanvardbackwardr

.fin 3e..feet on toes

bat at the crease

is?. 3 ~ . back

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fig.3i. Rotate @Ian view representation)

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right + 0 + l e e (904 j i ......,......

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fig.3k Twist

Finrre 3. Illustration ofthe bo& and the bat orientation for a rizht-handed batsman. described from the crease. rroceeamgs NEE Southeastcon ZUUJ

142

to allow swing of to h n t foot On drive Over the ball ball and initiates hand, adding

stroke. power. bat. during follow bent)' through. Moves back and

On ball ofback acmss the line of the ball, pointing fool bent) square towards point On big toe, leg extended' May slide up on big loe foot (bee

during follow through..

Lead and then leans Takes bat up and to d i ~ t i o n ofstroke wmpliments bottom arm fully

hand extended.

. Initiates stroke, On big tw, extended. square cut

On ball of front

bent).

Fomard to pitch Brings bat on line of Compliments top

stroke. power. ~l;aight drive Over the ball ball and initiates hand, adding ofball, knee bent to front foot

~~~~",",",",';b,, Across to inside Takes bat up and Initiates stroke, (on big tae or line ofball, On ball of back

lifled up), pointing down foot The hook Inside line ofball compliments bottom arm fully hand extended. Remaining on big pitch, then pivots

toe for balance.

Pulled back to Takes bat up and Initiates stroke, pointing down

lo sqvan leg'

On ball of back foot prior to

stroke, on ball offront foot afler

Back and across to impact of The pull inside line ofball compliments bottom arm fully pitch. On big toe

ball of foot afler

On or j u t inside the ~ . ~ ~ ~ ~ ~ m Slide down pitch On tws, knee bent 2;: zzt line ofthc ball hand of ball, knee bent :g;dng the foot and toes of

hand extended. prior to Contact, 0"ONS"P

stroke The swecp back faot.

Tablc 1. Classification ofcricket batting strokes based OD body positions

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Sboke Name Mode Ball Bowled Bat Orientatlon Ball contact on Bat

Middle 0' vertical, O'-lSD horizontal, bat Back foot off drive Attacking Short, on or just outside 08sNmp. seaiaht to ball thmugh mid off

all wide ofoff SNmp and

Attacking

Attaclting

On drive

square cut

I I

Leg glance (back foot) side guided behind square Attacking Short pitched ball, going dawn leg 0' vertical, -6Oo-(-90@l horizontal, ball is Middle

Halfvolley pitched on or just in line with leg shlmp Short pitched ball wide off sNmp and -90' vcrtical, swing thmugh horizontal, ouncing higher than the sNmps

0' vertical, -3Oo-(4S@l horizontal, ball angled towards mid on

bat tilled to keep face down

Middle

Middle

steady in horizontal plane, swing in the vertical plane

-90' vertical, swing thmugh horizontal, contact made at 90' horizontal

Middle Straight drive Attacking Half volley on sNmps

Middle Attacking Short pitched ball rising above chest height The hook

/The pull ]Attacking lhng hop waist high 90' ver(leal, swing thmugh horizontal, I Middle I iontact ;de at 0' horizontal

Table 2. Classification ofcricket stmkes. b&d on ballhat position

Table 1 and table 2 show mainly the motion of the batsman the moment the ball makes contact with the bat. It is important to examine what happens before and after this point. The stroke is thus described (figure 4) from the moment the bowler starts the run up process until the ball is deflected from the bat and the motion has ended. We have divided this time into three intervals namely; the waiting state, the receiving state, the playing and follow through state. The waiting state describes the batsman taking up his position at the crease to face the bowler. The receiving state starts when the bowler releases the ball and the batsman is now moving to fmd the best position to play the selected shot. (It is during this period that the batsman decides on the hest stroke to play for the particular ball being bowled). The ball making contact on the bat and the batsman's orientation of the bat to play the stroke to the point where the ball leaves the bat and the bat is to be returned to the crease describes the playing and follow through states.

that the head would make if it were moved in the vertical plane relative to the head being centre as zero degrees.

Using figure 5 along with the specific descriptions in table 1 and table 2 we obtain fuzzy sets [11,12]. The fuzzy sets are more descriptive and they show the proper association for each member of each set. This provides for each stroke a closer to buman description of all the elements and now a better means for measuring them can be realized. The fuzzy sets for each state is described and hence the transition from one state to the next can be realized. The following fuzzy sets and the membership values for the cover drive and the forward defensive strokes are outlined in table 3. These are as follows;

Head vertical (level, up, down) Head horizontal {center, left. right} Front foot (forward, backward, at the crease, down thepitch. square. right, lejt) Baek foot (forward, backward, at the crease, down the pitch, square, right, leff} Bat {back I$, forwardswing, rotate right, rotate le)?, swing right, swing le@, twisted right, twisted left}

Figure 5 is a graphical illustration for the range of motion the head and the feet over the four temporal states described above. For the head up and the bead down set. The angles are those that the chin would make if it were moved in the vertical plane. The bead level is that angle when the chin is parallel to the ground (07. The head right and head left are the angles

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I .oo

0.50

0.00

Waiting Receiving Playing

Figure 4. Graphical illustration ofternpard states.

Head down Head level

. . . . . . . . . . . .

. . . . . 50 70 90

angle (degrees)

Figure Sa vertical head positions

Foot bpckwards at crease F o p forward

Head left Head center Head rieht . . . . . . . . . . . . . . . . . . . . . . . . . : : : : :

. . . . . . . . . . . . . . . . . . . . . . . . . . .

-90 -70 -50 -30 -10 10 30 50 10 ' 90 angle (degrees)

Figure 5b horizontal head positions

Fool forward Foot bpkwards at crease

: : : : :

-100 -80 -60 -40 -20 0 20 40 60 -60 -40 -20 0 20 40 60 80 100

Distance. J relative to the crease Distance. J relative to the crease

Figure 5c back foot Figure5d front foot

Figure 5. An illustration of the range of motions for the four temporal states. 5a and Sb show the possible head positions, while 5c and 5d show those for feet positions.

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1

By analyzing these fuzzy sets for each state of the motion and then combining them base on the temporal states outlined, we obtain the rules for each stroke. There are two IeveIs to the rules, the fust gives the compositions of the fuzzy sets in each temporal state and second is a combination of the temporal states. Thus the rules for the Cover Drive can thus be Written. The temporal states are represented as follows, w = waiting, r =receiving, and p =playing, hence cover (w) = refers to the cover drive in the waiting state.

Level 1 Rules Cover (w) =Head straight AND Front foot at the crease AND Back foot a t the crease AND Bat at the crease Cover (1) =Head slightly down AND Front foot slightly forward AND Front foot a bit square AND Back foot slightly behind the crease AND Back foot slight tipping AND Bat have a slight back lift. Cover (p) = Head over the ball AND Front foot forward AND Front foot more square AND

Back foot at the crease AND Bat move slightly

Proceedings IEEE SoutheastCon 2003 146

forward, AND Bat rotated a bit right AND Bat twisted a bit to the right.

Notice that the sets described are a combination of the sets listed in the table via their membership functions. For example; Head straight is a combination of the fuzzy sets level, center and head le@, and Head slightly down is a combination of the sets level, down, center and left. Level 2 Rules. Cover drive = cover (p) FOLLOWING cover (I) FOLLOWING cover (w)

Notice that Table 3 only shows sets that can be considered as part of the batsman’s motion. The type of ball being bowled, although it is of critical importance to the stroke being played, is not considered in table 3. It does influence the batsman’s motion but is not a part of hisher motion. The grip, and the weight distribution on feet although linked, to the batsman’s motion are not as yet included in table 3. Force sensors are force mats needed to be able to give accurate measurements of all the elements involved in the gripping of the bat and weight distribution respectively. The current measurement system that we are using consists of positional sensors and will need modifications to include inputs fkom other sensors.

Conclusions and further work Within th is paper we have proposed a system to analyse cricket-batting strokes and to aid batsmen to perform more efficiently. We employ the use of electromagnetic sensors to analyse a sequence of instantaneously static postures at different times during the stroke. Cleary the use of the wires for the sensors will limit the range of motion of the batsmanhatswoman. The Startrak system which is wireless will solve this problem. The classification presented for body position, using fuzzy set theory, forms the initial guide to the formulation and design of the analysis system. Work continues to introduce further fuzzy classifications for the other important factors in the development of the expert system such as body weight distribution, grip, type of ball bowled etc. SO far we have only looked at classifying batting strokes played against pace (fast) bowling and have not considered spin (slow) bowling. The incorporation of slow bowling into the system will require futher classification of the different batting strokes played against slow bowlers. Markov chains are being investigated as means of analysing the temporal progression.

Acknowledgments We wish to thank the Jamaican cricket Board for their support through providing batsmen and the future use of equipment, coaches and the Sabina Park cricket ground. We also wish to thank the West Indies Cricket Board for their support and Mr. Hugh Rose who has acted as a general cricket advisor to the project so far. We would particularly like to thank MI Brian Breeze, CEO Sabina Park Cricket Ground and Mr Dennis Miller for contributing greatly with the physiological classification of the batting strokes.

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