FIP, or fielding independent pitching, estimates a pitcher’s ERA using only the outcomes he controls on his own: strikeouts, walks, hit batters and home runs. It strips out balls in play, where defense and luck take over, and is scaled so a FIP reads just like an ERA. A pitcher whose ERA is well below his FIP has often been lucky, and one whose ERA is well above it has often been unlucky.
FIP vs. ERA
| ERA | FIP | |
|---|---|---|
| Measures | Earned runs allowed per nine innings | Expected runs based on K, BB, HBP and HR |
| Affected by defense | Yes | No |
| Affected by luck on balls in play | Yes | No |
| Best use | What actually happened | What is likely to happen next |
| Stability | Swings more year to year | Steadier and more predictive |
Why Home Runs Weigh So Much
Each home run is multiplied by 13 in the formula, far more than walks or strikeouts, because a homer is the one batted ball outcome the defense cannot touch. That is why fly ball pitchers in small ballparks often carry a higher FIP than their ERA suggests. Related metrics like xFIP replace a pitcher’s actual home runs with a league average home run rate on fly balls.
For the basics of the stat FIP is modeled on, see what is a good ERA.
Related
What is BABIP · What is wRC+ · What is OPS · What is WAR · What is a good ERA
Formula and scale from the FanGraphs Sabermetrics Library.