Thursday, August 6, 2015

Visualizing Momentum

Momentum has been described as an "invisible" or "hidden force" in tennis.  (See "The Hidden Force" and the NYT article "The Importance of Momentum in Tennis").  Whether momentum actually exists at all in Tennis or any other sport has long been debated, but it is a certainly that momentum is something that many players and even the crowd "feels" when watching a match.

In "Analyzing Wimbledon", Professors Klaassen and Magnus conclude via statistical analysis that some limited momentum exists for weaker players, but not for top players.

While it is impossible to fully capture the emotional and physical dynamics that contribute to changes in momentum, whether it exists or not, it is possible to create a representation of the progression of points throughout a match which includes details relevant to the outcome of each point.

The following graphic captures the outcome of first and second serves, the return of serve, the Key Shot which determines a point winner, as well as the length of the rally, if any, while a point is being played.  The centerline which runs down the middle of the graphic represents an even point score and the line moves left or right depending on which player has won the most points; a standard score-matrix is overlaid to give an understanding of the outcome of each game.

For a full explanation of how to read this graphic, please see my post on the GameFish, which was derived from the Momentum Chart.

Winning the most points does not, however, insure that a player will win a match.  Psychological factors aside, in certain cases when a point is won is more important than the fact that a point was won, at least with respect to the match outcome.  I will discuss this in a future post and hopefully have some visuals which can facilitate better understanding this point.  At the moment I'm working on a graphic that merges the basis of the Momentum Chart (difference in total points) with idea of the "Points-to-Set" graph (number of points required to win, at any given moment) and I'm hoping it will provide some insight.

The Momentum Chart in TAVA was inspired by the excellent Momentum Chart in the ProTracker Tennis App (for iPhones/iPads).  ProTracker Tennis has a few features which I didn't incorporate in my Proof-of-Concept version.  The score-matrix overlay is original to my implementation.

Version 2 of TAVA will increase the use of the Momentum Chart as a control structure and seek to overlay visualizations which provide additional analysis into factors which may be seen to have an influence on changes in momentum.  At the moment the Momentum Chart drives the Court View (post forthcoming) which displays shots for matches captured with ProTracker Tennis.

There is an excellent discussion of Momentum for Players and Coaches on the Turbo Tennis blog at The Tennis Server.  Please see the articles "Momentum... Swing it in your favor",  "Momentum Revisited" and "The Big MO!".

Of course, Momentum can also be interpreted in the context of a series of matches.  The cross-match visualizations I'm doing for the next version of TAVA will look at this aspect of Momentum in depth.

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