What is RE24?

RE24 Definition

The baseball statistic RE24 stands for run expectancy based on 24 base-out states. While that is a bit of a mouthful, this stat isn’t as complicated as it may seem at first. In this article, we are going to walk through the basics of RE24 to help you understand how this stat can be used to evaluate players. 

Before we get started, it’s important to note that this is one of the few stats which can be used to evaluate both hitters and pitchers. Most statistics are focused specifically on hitters or pitchers (or defenders), but few cross the line to cover both sides of the game. Whether you want to assess the performance of a hitter or a pitcher, RE24 is something you can turn to for help. 

Also of note, this is a counting stat, which accumulates as the season moves along (as opposed to a rate stat, such as batting average). A player will add to or subtract from his RE24 total with each completed plate appearance, so it is important to keep in mind the time frame you are evaluating when using this metric. Commonly, it will be used over a full season, but could even be used over the span of several seasons. 

The Concept of RE24

At the heart of RE24 are the 24 possible base-out states that exist in this game. We need to take a moment to clarify what the base-out states are, and why they are important, before we can get into the specifics of RE24. 

Given that there are three bases which can be occupied at any given time during the game, there are a total of eight base runner configurations possible. Those are as follows –

  • Bases empty
  • Runner on first
  • Runner on second
  • Runner on third
  • Runners on first and second
  • Runners on first and third
  • Runners on second and third
  • Bases loaded

Each of those configurations can take place with zero outs, one out, or two outs. When you add it all up, you are left with a total of 24 base-out states. 

So, why are base-out states an important concept in baseball statistics? They provide useful context for the game thanks to something known as a run expectancy table. This table offers an expected number of runs to be scored in the inning based on the base-out state. Knowing what the statistics indicate is the likely number of runs scored from any given 

As you might expect, fewer outs and more base runners is going to increase the run expectancy for the offense. For instance, the run expectancy from a base-out state of no outs and bases loaded is going to be far higher than the expectancy from two outs and bases empty. While run expectancy charts can be produced based on league-wide statistics for any given period of time, they are more accurate when using ballpark-specific data. 

Bases 0 Outs 1 Out 2 Outs
_ _ _ 0.4886 0.263 0.1008
_ _ 3 1.3081 0.8977 0.3634
_ 2 _ 1.0732 0.6551 0.3187
_ 2 3 1.8927 1.2898 0.5813
1 _ _ 0.8577 0.5115 0.2213
1 _ 3 1.6772 1.1462 0.4839
1 2 _ 1.4423 0.9036 0.4392
1 2 3 2.2618 1.5383 0.7018

The above table is a run expectancy matrix on a league-wide basis for the 2012 season. Information courtesy New English D.

How is RE24 Calculated?

Now that we have a big picture understanding of what RE24 is, let’s get into the details of how it is calculated. Fortunately, the calculations are quite simple. The number we are after here is the difference between the beginning run state (prior to an at-bat) and the end run state (after an at-bat). So, the calculation for hitters is as follows – 

RE24 = RE End State – RE Beginning State

If working on an RE24 for a pitcher, it would be reversed – 

RE24 = RE Beginning State – RE End State

Using a run expectancy table, the end state number will be determined based on the combination of outs and base runners after an at-bat has been completed. From that number will be subtracted the beginning RE state number, to leave a difference. If the run expectancy for the offense has been improved, the resulting RE24 number will be positive. If it has been reduced, the RE24 number will be negative. 

But wait! The calculation above is just about finished, but it needs one more step – any runs that were scored as a result of the at-bat. If a batter knocked in two runs with a base hit, those two runs need to be added to the RE24 calculation to make it accurate. For a pitcher, runs scored would be subtracted away from the total. This is another simple step, but an important one. 

To make sure this is clear in how it is applied, let’s work through two examples – one for a hitter and one for a pitcher. We will use the numbers in the matrix from earlier for the purposes of these examples. 

For our hitter, let’s imagine he comes to bat with runners on first and second and no one out. Our matrix indicates the run expectancy for such a situation in 2012 was 1.4423. The batter then hits a double, scoring both of the base runners in the process. So, the new base state is a runner on second and still no one out, which has a run expectancy of 1.0732. With that info, we can calculate the batters RE24 for this at-bat. 

RE24 = 1.0732 – 1.4423 + 2 = 1.6309

The batter would have increased his overall RE24 by 1.6309 as a result of hitting a two-run double. 

Moving on to the pitcher, imagine a situation where the bases are loaded with one out. In that situation, run expectancy would sit at 1.5383 according to our table. The pitcher manages to strike out the hitter, moving the situation to bases loaded and two outs, which has an RE of 0.7018. The math here is simple – 

RE24 = 1.5383 – 0.7018 = 0.8365

Needless to say, striking a batter out with the bases loaded and one out is a big accomplishment, and the pitcher is rewarded accordingly. 

Why is RE24 Important?

RE24 can be a helpful stat largely because it offers context to performance. Rather than measuring the player’s performance simply in terms of raw stats like home runs, strikeouts, etc., RE24 goes a little deeper to consider the context of the surrounding game. Is a player performing in a way that is helping his team move closer to victory? A quality RE24 number indicates that a player has frequently put his team in a better position by moving the run expectancy table in the right direction (higher for a hitter, lower for a pitcher). 

What is a Good RE24?

With all stats, it’s helpful to know what’s good, what’s bad, and what falls in the middle. Like many advanced statistics, RE24 is set to zero as average. That’s a handy little aspect of this statistic, as you can immediately know if a player has been above or below average on this metric just by seeing if their number is positive or negative. Anything over zero is above average, and anything under zero is below average. 

So, a positive number means a player is above average compared to his Major League peers, but how high should that number go? For a hitter, an RE24 in the teens is a solid performance, while moving up into the 30s and 40s is All-Star caliber play. For starting pitchers, those numbers are a bit lower, as they don’t have the opportunity to be on the field as frequently. In that case, an RE24 above 20 would be an excellent effort. 

As always, looking to Mike Trout as the gold standard is a good idea when learning about RE24. In each of his first seven full seasons in the big leagues, Trout surpassed 50 in RE24. Needless to say, that is an incredible achievement, and one which is unlikely to be matched anytime soon. 

For a little more context, let’s look at a list of the 10-best RE24 seasons since the turn of the century. 

Barry Bonds 2004 128.94
Barry Bonds 2001 118.93
Barry Bonds 2002 118.51
Todd Helton 2000 93.18
Jason Giambi 2000 91.61
Sammy Sosa 2001 90.66
Jason Giambi 2001 90.6
Barry Bonds 2003 84.65
Alex Rodriguez 2007 84.36
Carlos Delgado 2000 84.15

What are the Problems with RE24?

RE24 is a helpful statistic designed to bring context into player performance for both pitchers and hitters. Like all stats, however, it has its flaws. For one thing, defense is not considered in the calculations, so all responsibility for run prevention is assigned to the pitcher. Also, the only component of baserunning that plays a role in the stat is stolen bases, which is an incomplete picture of how much value a player adds through baserunning skill. 

One other thing to point out here is the limited scope of the context that RE24 applies to the game. Yes, it accounts for player performance in terms of changing run expectancy, but it does not deal with score or inning in any way. So, for example, a two-out grand slam to take the lead in the ninth inning is treated the same as a two-out grand slam in a game that was already a blowout. If you are looking for a way to measure the ‘clutch’ performance of a given player, RE24 will not be able to provide you with that information.