LevI Leverage Index - A value of 1.00 indicates this player appeared in plays of average importance. Above 1.00 indicates they had higher than normal importance (for example, a closer typically has leverage around 1.8). A mopup pitcher, on the other hand, will have a likely LevI of much less than one. This value is not adjusted for league run scoring and park effects. (numbers provided by Tom Tango and InsideTheBook.com)
Leverage Splits - High Leverage is a value over 1.5 (20% of plays). Medium is 0.7 to 1.5 (about 40% of plays). Low is less than 0.7 (about 40% of plays).
WPA Win Probability Added - The sum of all win probability added (or subtracted) when this pitcher was on the mound or this player was at bat (note baserunning is not yet assigned to the baserunners). A positive number means they contributed more than they subtracted from their team's possibility of a win. This value is adjusted for league run scoring and park effects. (numbers provided by Tom Tango and InsideTheBook.com)
wWPA - winner's Win Probability Added - The win probability added or subtracted (if negative) by this single play from the eventual winning team's win expectancy. This value is adjusted for league run scoring and park effects. (numbers provided by Tom Tango and InsideTheBook.com)
wWE - winner's Win Expectancy - The current probability (after the play) of the eventual winner winning at this point in the game. Note these are rounded, so a probability of 100% before the last play means it is close, but not quite 100%. This value is adjusted for league run scoring and park effects. (numbers provided by Tom Tango and InsideTheBook.com)
Win Probability Added statistics are tools that have been created by a number of sabermetricians including the Mills Brothers (Eldon and Harlan), Doug Drinen, and most recently Tom Tango. These statistics generally look at the game context at the start and the end of the play and compare the batting team's probability of winning the game in both situations.
For example, in the top of the eighth, the visiting team might be down five with one out and runners on first and second. The batter then hits a home run to bring the visiting team to within two runs, still with one out, but now with no runners on base. Prior to the home run, the batting team had about a 3% chance of winning which improved to 10% following the home run. This change of 7% is credited to the batter and debited to the pitcher. Compute these for every play and every game from 1956 on and you have win probability added stats.
This stat does something that a lot of people criticize many advanced stats for not doing. It considers the context of the game. A home run with the score tied is worth much, much more than a home run with a ten-run lead. In fact, a walk or run scoring ground out in a tie game is worth more than a home run in a blowout.
Our win probabilities are computed using work by Tom Tango and a description can be found in this article. Typically these calculations involve a lot of math and simulation, but Tom and myself do the heavy lifting for you.
Stats updated through August 20, 2008.
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