Tuesday, November 17, 2015

Rally Tree: Point Distribution and Win Percentage

Tennis is an "intermittent" sport.  The level of intensity can vary greatly with the rally length of points and the time taken between points (among other factors including surface, ball type, sex and level of play).  When rallies are visualized they are typically depicted temporally from the first point to the last, which gives a jagged chart where it is difficult to discern any pattern at all.  "Rally Tree" is an attempt to bring a different perspective to the analysis of rallies.

 "Rally Tree" depicts the distribution of points across various rally lengths, beginning at the top with rally lengths of Zero, which indicate either Aces, Serve Winners, or Double Faults. Color coding differentiates errors where balls were "netted" vs. hit long.

There are several available views. The default view displays all points for a single match or selection of matches. You can filter by player to display only points served by either player (or composite of opponents).  Notice the number of winners among the points won for servers vs. those receiving.

Additionally there is an overlay depicting the percentage chance that a point was won for any given rally length. The offset vertical lines represent 50% either side of center (0%).
For the "served points" views, this gives a graphic representation of the Persistence of Server Advantage, which varies greatly among players. Please note that this is not the same as percentage of points won for a given rally length.
The "Rally Tree" graphics in this post are of Novak Djokovic's matches at Wimbledon in 2014 and 2015. The last two images depict the persistence of Djokovic's server advantage on the left and a composite of his opponents' server advantage on the left. Djokovic's dominance is obvious.  Apart from rallies of seven, he had a greater than 50% chance of winning all points with rallies up to sixteen.  His opponents' composite server advantage only extended to rallies of five.

You can play around with a live version of Rally Tree and explore your favorite players at TennisVisuals.com

In the near future "Rally Tree" will be integrated with "Game Tree" and other TAVA components so that selections in one component can drive views in another.  For instance, a "Point Progression" from 0-0 to 0-15 can be selected in "Game Tree" to view the distribution of points in the "Rally Tree" or "Points-to-Set".  From this point it will be possible to explore whether there are certain points in a match when rally lengths increase...

To read more about "Persistence of Server Advantage" please follow the link to Jeff Sackmann's blog post on the topic.

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