18 October 2007

Quantifying baseball excitement

Playoff baseball is a crapshoot.  So few games are played in a series that the better team loses fairly often, so it'sn't exactly the fairest way to determine a champion.  But its unpredictability and the fact that every game means so much make baseball in October fun to watch.

Fan Graphs is a fun site that offers visual representations of baseball games, estimating each team's probability of winning the game before and after each play and plotting the resulting curve through all 9+ innings, finally approaching 100% for the winning team.  Underneath each graph is the Leverage Index, a measure of the importance of each game situation.

For example, consider the games of October 12th.  In the first game of the ALCS, the Red Sox took a four-run lead in the bottom of the third and the Indians' chances of winning were slim for the rest of the game.  The Leverage Index was also low the rest of the game, meaning that each individual play had little potential effect on the outcome.  Not a very exciting game.

In the second game of the NLCS, the Diamondbacks fell behind by one run three times and scored to tie it again twice, failing only in the bottom of the eleventh.  It was a close game the whole way and the Leverage Index was especially high in the last three innings—very exciting, with much riding on each play.

The next night, the Indians and Red Sox traded the lead several times until the Indians scored 7 runs in the 11th inning and won 13-6.  Exciting until Trot Nixon's RBI single.

But regular-season baseball can be exciting too.  Take September 22nd, surely the most exciting single day of games this season.  In five games, a team had less than a 25% chance of winning its game but ended up coming back to take it.  The Orioles were behind the Rangers 6-2 and 8-5 but came back to win 11-9.  The Phillies and Nationals were tied 1-1 in the bottom of the 7th and the Nationals had a runner on third with none out but couldn't score; the Phillies finally won 4-1 in 10 innings.  The Brewers went into extra innings against the Braves, scoring one run in the top of the tenth, but the Braves scored one in the tenth and again in the eleventh to win it.  The Red Sox were ahead of the Devil Rays 5-2, then down 6-5, then scored three in the ninth to win it 8-6.  And the Blue Jays were behind the Yankees 6-3, then went up 8-6, then down 9-8, then up 11-9, then lost 12-11 in 10 innings.

(The Blue Jays won especially exciting games on May 26th and July 8th.)


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