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• O-Swing%: The percentage of pitches a batter swings at outside the strike zone.
• Z-Swing%: The percentage of pitches a batter swings at inside the strike zone.
• Swing%: The overall percentage of pitches a batter swings at.
• O-Contact%: The percentage of pitches a batter makes contact with outside the strike zone when swinging the bat.
• Z-Contact%: The percentage of pitches a batter makes contact with inside the strike zone when swinging the bat.
• Contact%: The overall percentage of a batter makes contact with when swinging the bat.
• Zone%: The overall percentage of pitches a batter sees inside the strike zone.

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RC/27:

A stat created by Bill James to measure how many runs a lineup of 9
of the same individual would score in a game.

A = H + BB + HB - CS - GDP
B = TB + .52 * (SB + SH + SF) + .26 * (BB + HB - IBB)
C = AB + BB + HB + SH + SF

RC = A * B / C
O = AB - H + CS + GDP + SH + SF
RC/27 = RC / O * 27

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BRAA: Batting Runs Above Average. The number of runs better than a hitter with a .260 EQA (i.e., an average hitter) and the same number of outs; EQR - 5 * OUT * .260^2.5.

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EQA:

Equivalent Average. A measure of total offensive value per out, with corrections for league offensive level, home park, and team pitching. EQA considers batting as well as baserunning, but not the value of a position player's defense. The EqA adjusted for all-time also has a correction for league difficulty. The scale is deliberately set to approximate that of batting average. League average EqA is always equal to .260. EqA is derived from Raw EqA, which is (H + TB + 1.5*(BB + HBP + SB) + SH + SF) divided by (AB + BB + HBP + SH + SF + CS + SB). REqA is then normalized to account for league difficulty and scale

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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.

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.

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WPA/LI

(context neutral wins / game state linear weights): How many wins a player contributes to his team with the Leverage Index aspect removed, invented by Tom Tango.

Calculating WPA/LI: WPA is divided by LI for each individual play attributed to a specific player and then the WPA/LI for the individual plays is then added up to create WPA/LI for an entire season. This is considerably different then taking a player’s WPA and dividing it by pLI.

Why you should care: Unlike standard linear weights, WPA/LI does take into account the situation. So at times when a walk would be just as valuable as a home run, WPA/LI accurately weights the walk and the home run, where linear weights would still give .13 wins to the home run and the walk .03 wins.

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WPA (win probability added): WPA is the difference in win expectancy (WE) 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’ WPA for individual plays is added up to get his season total WPA.