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Licensed Unlicensed Requires Authentication Published by De Gruyter October 12, 2019

Shot-by-shot stochastic modeling of individual tennis points

  • Calvin Michael Floyd EMAIL logo , Matthew Hoffman and Ernest Fokoue

Abstract

Individual tennis points evolve over time and space, as each of the two opposing players are constantly reacting and positioning themselves in response to strikes of the ball. However, these reactions are diminished into simple tally statistics such as the amount of winners or unforced errors a player has. In this paper, a new way is proposed to evaluate how an individual tennis point is evolving, by measuring how many points a player can expect from each shot, given who struck the shot and where both players are located. This measurement, named “Expected Shot Value” (ESV), derives from stochastically modeling each shot of individual tennis points. The modeling will take place on multiple resolutions, differentiating between the continuous player movement and discrete events such as strikes occurring and duration of shots ending. Multi-resolution stochastic modeling allows for the incorporation of information-rich spatiotemporal player-tracking data, while allowing for computational tractability on large amounts of data. In addition to estimating ESV, this methodology will be able to identify the strengths and weaknesses of specific players, which will have the ability to guide a player’s in-match strategy.

A Appendix

A.1 Theoretical ESV

Letting T(ω) denote the time at which a point following the path ω ends, the point’s outcome for player i then is a deterministic function of the full resolution data at this time, Γi(ω)=hi(ZT(ω)(ω)). The expectation 𝔼[Γi(ω)|t(Z)] is an integral over the distribution of future paths the current point can take. Recall our definition of Γi(ω) such that Γi(ω)=hi(ZT(ω)(ω)). Thus, evaluating ESV amounts to integrating over the joint distribution of [T(ω),ZT(ω)]:

(8)νti(ω)=𝔼[Γi(ω)|t(Z)]=t𝒵hi(z)(Zs(ω)=z|T(ω)=s,t(Z))(T(ω)=s|t(Z))dzds.

A.2 Additional time notations

The notations τt and δt will be defined as:

(9)τt={max{s:s<t,Cs(ω)𝒞ServerShot}+ε,if Ct(ω)𝒞ServerShotmax{s:s<t,Cs(ω)𝒞ReceiverShot}+ε, if Ct(ω)𝒞ReceiverShot
(10)δt={min{s:s>τt,Cs(ω)𝒞ServerShot},if Ct(ω)𝒞ServerShotmin{s:s>τt,Cs(ω)𝒞ReceiverShot},if Ct(ω)𝒞ReceiverShot

where ε is the temporal resolution of the player-tracking data. In this case, ε will be equal to 1/25 s.

A.3 Strike/return subset definitions

  1. Let 𝒮 contain every strike contained in the dataset, which includes who struck the shot, its strike state and its corresponding strike category.

    1. 𝒮={player ID}×{𝒫}×{ΛSC}

  2. Si𝒮 : The subset of all strikes in 𝒮 struck by player i.

  3. SβSi𝒮 : The subset of all strikes in 𝒮 struck by player i from the strike state βS𝒫.

  4. SβS,λSCi𝒮 : The subset of all strikes in 𝒮 struck by player i from the strike state βS, with the strike category λSCΛSC.

  5. Let contain every return contained in the dataset, which includes who is returning the shot, its return state and its corresponding return category.

    1. ={player ID}×{𝒫}×{ΛRC}

  6. Ri : The subset of all returns in returned by player i.

  7. RβRi : The subset of all returns in returned by player i from the return state βR𝒫.

  8. RβR,λRCi : The subset of all returns in returned by player i from the return state βR, with the return category λRCΛRC.

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Published Online: 2019-10-12
Published in Print: 2020-03-26

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