## RE24

RE24 (or run expectancy based on the 24 base-out states) may sound like a computer error or a random assortment of letters and numbers, but the actual logic and mechanisms behind the statistic make it extremely useful for fans and analysts. It is based on the concept of run expectancy, which provides the average number of expected runs per inning given the current number of outs and placement of baserunners. The number “24” refers to the potential number of base-out states (zero, one, two outs and eight different baserunner arrangements).

Since run expectancy tells you the number of expected runs, any number of runs created above or below that value can be treated as runs above or below average for the batter or pitcher depending on the outcome of each plate appearance. Unlike wRAA, wRC, or Batting Runs, RE24 is context-dependent and assigns more credit for hits with men on base than with the bases empty. With league average set to 0, hitters with positive RE24 are creating more runs than we would expect given the situations they have been placed in and pitchers with positive numbers are preventing more runs than average given the situations in which they have been placed.

On the hitting side, RE24 is a measure of how well hitters are capitalizing on their opportunities while also not assigning extra credit (like RBI) to hitters who happen to come to the plate with men on base very often. For pitchers, particularly relievers, RE24 is useful because it allows for multiple pitchers to share credit for allowing a baserunner to score and assigns credit to pitchers who strand the runners of the pitcher they relieved.

Calculation:

Calculating RE24 for a specific play or game is extremely easy as long as you are working with the appropriate run expectancy matrix. A run expectancy matrix presents the expected number of runs scored between a given point and the end of an inning based on the overall run environment, the number of outs, and the placement of the baserunners. For example, in the RE matrix below (run environment set at 4.15 runs per game), the expected number of runs given a runner on first and no outs is 0.831 runs.

Runners 0 Outs 1 Out 2 Outs
Empty 0.461 0.243 0.095
1 _ _ 0.831 0.489 0.214
_ 2 _ 1.068 0.644 0.305
1 2 _ 1.373 0.908 0.343
_ _ 3 1.426 0.865 0.413
1 _ 3 1.798 1.140 0.471
_ 2 3 1.920 1.352 0.570
1 2 3 2.282 1.520 0.736

To calculate the RE24 of a given plate appearance, simply take the run expectancy of the result of the play, subtract the run expectancy of the the starting state, and add in any runs scored during the play. For example, if the play started with a man on first and no outs there was an original run expectancy of 0.831. If the batter hits a single that results in the runner getting to third and the batter ending on first, the resulting run expectancy would be 1.798. Since no runs were scored on the play, you would simply do the following:

1.798 – 0.831 + 0 = 0.967 RE24

A great thing about calculating RE24 is that whatever positive credit goes to the batter is mirrored exactly by the pitcher. So for allowing that single with a man on first, the pitcher would get -0.967 RE24. If a baserunner advances on a stolen base, wild pitch, or passed ball, the baserunner is credited with the RE24 and the pitcher is debited. In all other cases, the batter and pitcher are the only ones who are assigned credit for the play.

When runs are scored on the play, the calculation works the same way, but make sure you don’t forget to factor in the runs scored. So imagine that a batter singles with men on first and third and no outs (1.798 RE), moving us from that state to a state with men on first and second with no outs (1.373 RE).

1.373 – 1.798 + 1 = 0.575 RE24

As long as you have the proper matrix in front out you (there are unique ones for each park and year based on run scoring and the one presented above is roughly neutral for 2014), calculating this stat is a snap, even if the name makes it sound esoteric. This interactive tool allows you to change the run environment and calculate custom matrices. A player’s season RE24 is simply the sum of the individual RE24 values of each plate appearance of the season with total run values on par with what you might see in a stat such as wRAA.

Why RE24:

RE24 is valuable because it provides an answer to a different question than context-neutral run values like wRAA, wRC, and Batting Runs for hitters. If you want to know how frequently a batters hits a single or a double and how valuable his performance would have been in a neutral context, one of the other run value statistics is your best bet. Those stats tell you what happened in the batter’s box. RE24 tells you how what happened in the batter’s box impacted the context of the inning.

A batter who hit a double with two outs and the bases empty performed the same action as a batter who hit that double with the bases loaded, but the bases loaded double was much more productive given the situation. The bases empty double was worth about .2 runs above average while the bases loaded double was worth about 2.5 runs above average.

Whether you wish to use a context neutral or context dependent statistic is up to you. Generally, there is very little evidence that hitting with men on base is a unique skill independent of hitting in general, but there are good arguments for why using RE24 as a value metric is reasonable even if it isn’t a direct measure of skill. For example, looking at a player’s RE24 probably won’t be more predictive of a player’s future performance than looking at their wRAA, but when assigning retroactive credit, say in an MVP race, RE24 could make sense given your philosophical approach.

For pitchers, RE24 is scaled differently than our typical runs allowed metrics, so the comparison to context neutral statistics isn’t as obvious, but it provides a measure of how many runs above or below average each pitcher allowed given the state of the game. For starters, RE24 is only going to be particularly relevant when dealing with innings in which they were pulled from the game. All other innings will yield equivalent results to runs allowed because even if the pitcher gets docked for allowing runners to reach, they will be credited for stranding those same runners. For relievers, however, this is a very useful measure.

Relievers enter into games and leave games with men on base frequently, so the standard rule book definition of runs allowed doesn’t always capture a reliever’s true performance. For example, if a reliever enters with the bases loaded and no outs, stranding the runners and allowing all three to score have the exact same impact on that relievers RA9 or ERA. When using RE24, stranding the runners is worth 2.282 RE24 and allowing them to score and then getting out of the inning is worth -0.72 RE24.

For starting pitchers, you’re only going to notice significant differences if the starter is unusually lucky or unlucky with respect to how often their relievers allow inherited runners to score. There are a number of pitchers affected by that type of luck each year, but the value of RE24 remains more apparent when looking at relief pitchers.

How to Use RE24:

RE24 is very simple to use for hitters if you’re already familiar with runs above average numbers like wRAA. With league average set to zero, any positive value is that many runs above average and any negative value is that many runs below average. RE24 includes batting and between at bat baserunning (stolen base, wild pitches, etc), so if a player has 30.5 RE24, that means they were about 30 runs better than the average player would have been if given the same opportunities. Each win is worth between 9 and 10 runs depending on the year, so you can convert RE24 into wins by dividing it by that year’s runs per win. On FanGraphs, we call this REW instead of RE24.

Remember that RE24 is providing you with context adjusted runs, so when looking at this statistic you are measuring a player’s performance above or below average given the context in which they were placed. If you want to compare their context neutral stats with their context adjusted stats, an easy trick is to compare RE24 to Batting Runs plus wSB (or OFF minus UBR). This will allow you to see how well or poorly timed a hitter’s performance has been, but remember, context dependent numbers are less predictive of future performance than context neutral ones.

For pitchers, using RE24 in the language of RA9 or ERA is a bit trickier. You could simply learn to think in terms of runs above average for pitchers like you do for hitters, but the alternative is to take about 0.46 runs per inning and subtract the pitcher’s RE24 total to see it in terms of runs allowed. Then if you treat that new number as runs allowed and multiply be 9 and divide by innings pitcher, you’ll wind up with something akin to RE24 on a per 9 inning scale. Remember that RE24 is based on the run environment and park so this won’t be perfect. Remember also that while allowing runs is bad, a positive RE24 is good because it is a measure of runs better than average for pitchers. For starters, you won’t typically see dramatic differences, but for relievers you might.

Additionally, while RE24 controls for outs and baserunner placement, it does not make any adjustments based on the score of the game or the inning, meaning that a bases loaded situation is the same if the score is tied in the ninth inning or if the gap is seven runs in the fourth. In other words, while it controls for the likely number of runs, it does not control for how important those runs might be in the context of the game. RE24 also does not include any defensive value. All offensive events go to the hitter (or baserunner on steals) and all defensive events are credited to the pitcher. So while you can swap in RE24 for Batting Runs + wSB, you cannot look at a player’s RE24-Wins and call that WAR because it does not include all baserunning, any defense, any positional adjustment, or replacement level.

Context:

RE24 is measured in runs above average based on the current run environment, but since league average is always set to zero, the following rules of thumb apply:

Rules of Thumb

Rating RE24 (Hitters) RE24 SP RE24 RP
Excellent 45 25 15
Great 30 15 10
Above Average 15 10 5
Average 0 0 0
Below Average -5 -5 -5
Poor -10 -10 -10
Awful -20 -20 -15

Things to Remember:

● RE24 is based on the run expectancy matrix for the given park in a particular year, so while a neutral matrix like the one above will help you apply the concept, you might not be able to match RE24 values that we have on the leaderboards with your own calculations.

● RE24 only includes hitting and baserunning such as stolen bases and advancing on wild pitches for hitters. It does not include other baserunning, defense, position, or replacement level.

● RE24 assigns all defensive credit to the pitcher, so errors and bad defensive plays go against the pitcher as if the outcome of the play was caused by a sharp single.

● RE24 is context dependent by base-out state, but not by score or inning.

Links for Further Reading:

Get to Know RE24 – FanGraphs

RE24 – Inside The Book Blog

Context Batting Runs – FanGraphs

Introducing The Batter-Specific Run Expectancy Matrix – FanGraphs