Run Expectancy (RE24)

Simply put, RE24 is a statistic that credits (or debits) players for their role in changing their team’s odds of scoring (or preventing) runs in a given inning. This is a context-dependent stat that changes depending on the situation of the game.

Understanding The 24 ‘Base States’

There are 8 unique combinations of base occupancy that can occur during the course of a game. The bases can be empty… full… or any combination in between, as follows:

The other major variable to consider is the amount of outs there are when each ‘base state’ occurs. Thus, when you overlay the 8 base states with the 3 out states, 24 different possibilities arise.

All 24 of these base states are assigned a run expectancy value based on:

  1. How likely a run is to result based on the situation at hand
  2. The run environment of the game (i.e. The average amount of runs a team should expect to score in a game – runs / game).
BREW MATHs has taken care of all the scut work for you and has averaged every run expectancy for every base state since the steroid era ended (2003):
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Note how as the bases empty and outs accumulate, the likelihood of a run dwindles. The beauty of this statistic is that it can be applied to every plate appearance throughout the game. This allows you to figure out how valuable each player’s contributions is in real time:

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If a batter comes up with the bases loaded (1B / 2B / 3B) and NO OUTS, the stakes are as high as they can be (2.3067). If the pitcher strikes the hitter out, the next game state to follow will be bases loaded (1B / 2B / 3B) with ONE OUT. Therefore, each player is credited, as follows:

  • Pitcher: Gets POSITIVE credit for the play
    • 2.3067 – 1.5744 = +0.7323
  • Batter: Gets NEGATIVE credit for the play
    • 1.5744 – 2.3067 = -0.7323
  • NOTE: For every play, the pitcher and batter will score the inverse of the other.

As each play progresses, the players RE24 score either rises or falls, based on the situation and resulting outcome. Over the season, this adds up to a total score and allows you to compare each player to ‘MLB League Average.’ Scores above zero mean the player has generated (hitter) or saved (pitcher) that many expected runs. A negative score means that he has ‘given runs away’ when compared to the ‘statistically average’ player. A score of zero means that the player has performed exactly as you would expect, given the situations that they have faced.

Since the stat is CUMULATIVE or keeps accruing over a season / career, it will vary based on playing time and the player’s role within the team. Since relief pitchers play less than starters, they cannot be held to the same standard:

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2019 RE24 Leaders:


More recently, advances have been made to incorporate wOBA into the equation (follow this LINK to a Batter-Specific-Run Expectancy Tool)