Get to Know: Leverage Index

LI (leverage index): A measure of how important a particular situation is in a baseball game depending on the inning, score, outs, and number of players on base, created by Tom Tango.

Baselines: The average LI is 1 and is considered a neutral situation. 10% of all real game situations have a LI greater than 2, while 60% have a LI less than 1.

Why you should care: Because LI puts a single number on the importance of a situation, it creates a much simpler and specific way of determining which situations in games are important. It can also be applied to players. See below for various LI player stats:

pLI: A player’s average LI for all game events.
phLI: A batter’s average LI in only pinch hit events.
gmLI: A pitcher’s average LI when he enters the game.
inLI: A pitcher’s average LI at the start of each inning.
exLI: A pitcher’s average LI when exiting the game.

See Critical Situations: Part 3 for more details

Additional Links and Resources:

Critical Situations Part 1, Part 2, Part 3
Leverage Index Tables

David Appelman is the creator of FanGraphs.

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13 years ago

I absolutely love this site. Any suggestions as to how I might find game by game (game log) gmLI data for any given pitcher? Thanks. -Matt