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Tuesday, July 20, 2010

The Breakdown

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The Breakdown is an all-inclusive statistical tour of a college football game. In addition to computer simulated results, including scores, odds, team and individual statistics, the Breakdown sheds some light on the historical data and analytic techniques used to derive those predictions.

The first panel is a pre-game-post-game summary - an "Expected Box Score", including the expected score, odds, and team and individual statistics. Red and green numbers next to the team statistics compare the expected performance to the team's average performance. In this example, Texas' predicted 227 passing yard is 46 less than their season average, largely because the 59.4 completion percentage is 8 percentage points below their average. Individual predictions do not always account for injuries and suspensions, especially in-game injuries like that to Colt McCoy in this particular game.

Beginning in 2011, I have added a new tool. This second panel plots possible outcomes for a game. The darker the square, the more likely the outcome. For this game (now from the 2011 matchup between Alabama and Ole Miss), Alabama is heavily favored so most of the darkly colored dots fall above the diagonal line. The most likely outcome for this game is 38-7 Alabama (designated by the blue square). Alot each axis is the distribution for each team: Alabama will most likely score between 30 and 42 while Ole Miss will most likely score between 0 and 14.

The third panel is a summary of the two teams trend-O-meter, Hybrid, and cRPI (the cRPI* is multiplied by 100) - with national rankings in parentheses (I have now replaced the cRPI with the BPR). The hybrid rating is consistently among the reliable computer rankings, according to Massey's ranking comparison. You can see from the trend-O-meter that Alabama came into this game playing relatively well, but Texas did not.

Text boxes in this panel list more team statistics. Ratings (Unit, Rush and Pass) are adjusted to opponent strength. The unit rating is based on points scored/allowed, and the rush and pass ratings are based on yards/play gained/allowed. The bar graphs offer a summary of offensive and defensive match-ups. The portion below zero on each bar is representative of the opposing teams defensive strength in that area. The portion above the bar in the team's color is the predicted yards per run or pass for that team. The gray portion is what the team gains on average. In the title of the graph is percent of plays that the team runs or passes. In this case, Texas' defense should be particular effective against the Alabama pass offense, but because Alabama runs the ball 63% of the time, this advantage will not be as important. (Side-note: Alabama only allowed 46.8% completions that season, which is just disgusting.)

Panel 4 adds individual statistics and information on up to 6 previous meetings.

Next is a comparison of the two teams since 1980 (explanations of the Hybrid and cRPI). In this case, the hybrid ratings across seasons are standardized to range from zero to one.

The next panel has even more statistics and national rankings in parentheses. The most important numbers here are the sacks/pass, tackles for loss (TFL)/run, points/possession and TDs/possession. Here we see that deficiencies in the Texas offense were, in part, hidden because they averaged 14.3 possessions per game (given them more opportunities to score), and while they only averaged 5.2 plays/possession, they still averaged 2.7 points/possession, suggesting that many of the possessions started with good field position - a product of a very good defense (which only allowed 4.6 plays/possession).

Explanation of maps. In the maps, team's with similar styles are placed closed to one another. In this case, the number in parentheses is the point differential between what that team was expected to do and what they actually did. For example, in the "defense map: vs. Texas", we see that Nebraska and Oklahoma did better defensively against Texas than expected, and that Alabama is similar to these defenses, so that is an advantage for Alabama. On the other hand, the Texas offense is similar to offenses that did relatively well against Alabama (see "offense map: vs. Alabama"), so Alabama's advantage before is cancelled out. Moving down, we see that Texas is similar to defenses that performed relatively poorly against Alabama in Florida and Virginia Tech. This suggests that the Texas defense matches up poorly to Alabama's offense, so the net match up advantage in this game goes to Alabama. 

1 Comment:

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