Run Expectancy

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Run Expectancy (RE) is the expected number of runs scored in the remainder of an inning based on the base-out state. The pioneer of Run Expectancy was George Lindsey. Run Expectancy tables can be generated through empirical data, simulations, or Markov models.

A standard way of displaying RE values is an eight row by three column table with the the rows for the eight base states (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) and columns for the three out states (0 out, 1 out, and 2 out). Here's a chart for 1999-2002.

A frequency table from which the RE chart is generated is also useful when looking at 1-run strategies.

Run Expectancy is extremely useful in sabermetric analysis, for evaluating strategy and generating linear weight values. RE is closely related to Win Expectancy.