One of My Favorite Baseball Stats: RE24

One of my favorite baseball stats is one developed by sabermetrician Tom Tango and well explained by Patrick Jeter of Redleg Nation. It’s RE24, where “RE” stands for “Run Expectancy” and RE24 for “Run expectancy based on the 24 base-out states.”

In brief, it indicates how many runs, on average, a team can expect to score in an inning depending on the number of outs and which bases are occupied. For example, if a batter’s at the plate with the bases loaded and no outs, from that point to the inning’s end his team can expect to score more runs than if the same batter came to the plate with none on and the bases empty.

The key to determining about how many runs a team could expect to score is Tango’s RE24 matrix. Here’s a copy of the one in Jeter’s article:

The table contains eight rows and three columns. Each row contains one of the eight possible Bases Occupied states from none on (- – -) to bases loaded (1B 2B 3B). Each column contains an out situation: 0 outs, 1 out, or 2 outs. Combined, there are 24 Base/Out states.

The first Base/Out state is none on and no outs. When a batter came to the plate in that situation in the years 2010-2015, on average 0.481 runs scored from that point until inning’s end. Now, of course, it is impossible to score half a run. Think of it as meaning this: over 100 innings, 48 runs scored (again, on average) in that situation.

Say the first batter strikes out. When the second batter comes to the plate, the Run Expectancy is no longer 0.481 because though the bases are still empty, there is one out, so the run expectancy changed by -0.127 (0.481 – 0.254). Notice that in this case the result of the first plate appearance reduced the team’s Run Expectancy.

That change in Run Expectancy, -0.127, is part of its run value. It is how much the strikeout reduced the team’s chances of scoring. Further, that negative run value is added to the first batter’s run value total, his RE24 stat, decreasing it.

The second batter comes to the plate with an RE of 0.254 (one out, none on). Imagine that the second batter walks, giving the Base/Out state of one out and man on first. The Run Expectancy increases to 0.509 (one out, runner on first). The walk increased the RE24 by 0.255 (0.509 – 0.254). That increase is the run value of a batter reaching first base starting from the Base/Out state of one out and none on and ending with the one out, runner on first state.

Let’s look at one more situation. The third batter comes to the plate in the one out, man on first situation. That Run Expectancy is 0.509. He doubles, scoring the runner who was on first base. The Run Expectancy changes to 0.664 due to there now being a runner on second base with one out, so the run value of that double is 0.664 – 0.509 or 0.155 plus the run that scored, giving 1.155. That positive run value is added to the third batter’s RE24. So RE24 in this case is the change in the Run Expectation between two consecutive plate appearances plus any runs that scored, all in the same inning.

So what does a player’s RE24 for a number of games tell us? It reveals how many runs he helped to create by increasing the expectation that runs will score plus by any runs that actually result. An RE24 that is positive is above average, which is zero. An RE24 that is negative is below average.

Taking a look at the RE24 info on FanGraphs on July 26, 2016, Mike Trout is leading the Major Leagues with an RE24 of 46.33. That means he contributed to the scoring of 46.33 runs so far in 2016 above what was expected. The Met with the highest RE24, ranked #17, is Yoenis Cespedes with an RE24 of 26.52. Thus, he contributed toward the scoring of 19.81 fewer runs than Trout.

Overall this season, the Mets rank #24 with an RE24 of -21.23, one of 11 teams with a negative RE24. Thus they have scored 21.23 runs fewer than expected.

More on RE24

Patrick Jeter. RE24: A Primer

Tom Tango. Run Expectancy Matrix, 1950-2015

Neil Weinberg. The Beginner’s Guide To Deriving wOBA

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