Fielding Independent Pitching (FIP) is one of the more prominently featured statistics on FanGraphs and one of the bedrocks of sabermetric analysis. We all know that FIP is an imperfect measure of pitcher performance because it assumes average results on all balls in play, but we also know that it does a better job isolating the individual pitcher’s performance than simply looking at their ERA or RA9 because it only looks at strikeouts, walks, home runs, and hit batters. It’s a very informative tool, but it’s a metric derived from a subset of results.
When a pitcher’s ERA is significantly different from their FIP, the standard credo is that they were lucky or unlucky, but there are genuine reasons why a pitcher might have results that are better or worse than their FIP. To illustrate this, let’s take a peak at the biggest FIP over and under-performers of 2014.