Sunday, February 10, 2013

Accounting for Situational Hitting with RE24

Many fans grumble that statistics like OPS and Batting Runs don't account for situational hitting.  For example, if Tigers slugger Prince Fielder singles with a runners on second and third to drive home two runs, he gets the same credit as he would for a single with the bases empty.  Some will argue that this is not fair because he contributes more to his team in the former scenario than the latter.  In this post, I will introduce a statistic which accounts for a hitter's performance in different circumstances.

Traditional fans like to address situational hitting with the familiar Runs Batted In statistic, but that is a team dependent measure.  A player has more or less opportunity to drive in runs depending on who is batting in front of him.  Thus, a player gets acknowledged for driving home runs, but does not get penalized for failing to drive home runs.  So, the RBI count is not an adequate measure of situational hitting.

Other fans point to batting average with runners in scoring position, but that is based on a limited number of plate appearances.  It also doesn't consider the number of outs, the specific base runners (e.g. bases loaded versus second base only) or the type of hit (single, double, triple or home run).  Additionally, it ignores a player's performance when no runners are in scoring position. 

What we want is a statistic which gives a player credit for everything he does including situational hitting.  Batting Runs Above Average by the 24 Base/Out States (RE24) - found at FanGraphs - does just that.  The RE24 statistic is also sometimes referred to as "Value Added".  This metric will give a player credit for his singles, doubles, and all other events, and gives him extra credit for hits occurring with runners on base.  It even gives him points for a scenario which most other metrics ignore - moving a runner over with a ground out.  Conversely, it subtracts extra points for hitting into double plays.

In a recent post, I discussed just plain Batting Runs or Weighted Runs Above Average (wRAA) which is an estimate of how many runs a player contributed to his team beyond what an average hitter would have contributed in his place.  The RE24 metric is similar to wRAA except that it uses base/out states in the calculation.  An example of a base/out state is "runners at first and third and one out".  There are 24 possible base/out states and RE24 takes all of them into consideration.

In the calculation of wRAA, a double with the bases loaded and two outs counts the same (0.770 runs) as a double with the bases empty and no outs.  Conversely, RE24 counts the bases loaded double more than the bases empty double (2.544 versus 0.632) because it does more to increase the expected runs scored in the inning.

The RE24 metric for one at bat gives us the difference between run expectancy at the beginning and end of a play.  For example, suppose Fielder bats with a runner on first and one out. In that situation, we would expect 0.556 runs to score by the end of the inning.  Assume that Fielder then doubles, putting runners on second and third with one out. In that situation, we would expect 1.447 runs to score by the end of the inning. Therefore, Fielder's double is worth 0.891 runs.

Summing RE24 over all of a batter’s plate appearances yields his season total RE24. For
example, Fielder had a RE24 of 51 this year.  So, by that measure, he contributed 51 runs above what an average batter would have been expected to contribute given the same opportunities. This is a little higher than his 46 wRAA, which means that Fielder was especially good in situations with high run expectancy and added more to his team’s runs total than wRAA indicated.  We can estimate that he has contributed an extra 5 runs with his situational hitting.

Since situational hitting is largely (although not completely) random, RE24 is less predictive than wRAA and should not be used as a measure of ability.  It is, however, a good alternative to wRAA for looking at past performance.

Table 1 below shows us the RE24 in 2012 for some past and current Tigers.  Other columns in the table include, wRAA and the difference between RE24 and wRAA (RE24-BatRuns).  Fielder was the Tigers RE24 leader followed by Cabrera who had 47 RE24.  Cabrera was the runaway leader in wRAA (57), but cost the Tigers runs with situational hitting. Much of the reason for that was probably his high double play total.

Other Tigers who added value with situational hitting included Quintin Berry (+10) and newly acquired Torii Hunter (+6).  Other batters who tended to cost the Tigers runs in high-leverage situations were Delmon Young (-20) and Jhonny Peralta (-7).  Unlike Cabrera, those two did not hit well overall either.

Table 1: RE24 for Tigers (2012)

Hunter (LAA)
Infante (DET-FLO)

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