RE24 (runs above average by the 24 base/out states): RE24 is the difference in run expectancy (RE) between the start of the play and the end of the play. That difference is then credited/debited to the batter and the pitcher. Over the course of the season, each players’ RE24 for individual plays is added up to get his season total RE24.

Calculation Example: In game 4 of the 2007 World Series, the RE for the Red Sox to start the inning was .52. When Jacoby Ellsbury doubled off Aaron Cook in the very first at-bat in the game, the Red Sox were then expected to score 1.15 runs for the rest of the inning. The difference or RE24 was .63 runs. Ellsbury was credited +.63 runs and Aaron Cook credited with -.63 runs.

Why you should care: RE24 tells you how many runs a player contributed to his team. It’s similar to WPA (except in runs), but unlike WPA it does not take into account the inning or score of the game. Therefore, it is a more context neutral statistic. It does however take into account how many runners are on base and how many outs are left in the inning.

Variations: REW (run expectancy wins) is RE24 converted to wins.

Links and Resources:

Run Expectancy by Run Environment
The Book Wiki: Run Expectancy