A metric that determines the quality of a pitcher's performance by eliminating plate appearance outcomes that involve defensive play. The basic pitcher-dependent outcomes are home runs, walks and strikeouts.
In determining FIP, we use a concept very similar to the one used for Earned Run Average (ERA)...the primary difference being that pitcher ERA includes things that are not in the pitcher's power to control, namely defensive play. FIP gives us a look at how a pitcher performs in categories where it is basically a two-player game, pitcher vs. batter. An FIP of 3 or less is considered very good, while an FIP of 5 or over is thought of as very poor.
Each variable in the FIP formula is weighted based on importance/impact. A home run has by far the most impact, followed by walks and strikeouts. Historically, a pitcher's FIP does a much better job of predicting future performance than his ERA does.
Among the all-time leaders in FIP are Rube Waddell, Ed Walsh, Heinie Berger, Rube Vickers, Joe Wood, Addie Joss, Glenn Liebhardt, Chief Bender, Jack Pfiester and Christy Mathewson.