Fielding Independent Pitching or FIP measures what a player’s ERA should have looked like compared to what it actually is.
Pitchers have no control over what falls in for a hit or the level of defense being played behind them. FIP eliminates the randomness of balls in play and looks at stats that are controlled only by the pitcher and not by the fielders: home runs, walks and strikeouts.
FIP is given on an ERA scale and is a much better indicator of future performance.
Formula: (13*HR + 3*(BB+HBP-IBB) – 2*K)/IP + constant (2011 constant is 3.12)
The constant is solely to bring FIP onto an ERA scale and can be found by subtracting the league average FIP from the league average ERA.