Last night, I added FIP (short for Fielding Independent Pitching) to the site. This is a sabermetric stat for pitchers that approximates ERA without the effect of their team's fielding ability. FIP actually correlates to future ERA better than ERA itself making it a superior indicator of future performance.
The idea is that the pitcher most directly controls the number of walks, home runs and strikeouts that occur and that the batters and fielders have a bigger say on whether balls in play are turned into outs and that most pitchers' Batting Average on Balls in Play (BAbip) reverts to a league average from one year to the next.
FIP is (13*HR + 3*(BB+HBP) - 2*SO)/IP + Constant(year). The constant is set so the yearly avg FIP equals the yearly avg ERA.
FIP can be looked at exactly like ERA and is scaled to exactly the same league average as ERA, but it's range will be slightly smaller.
Often a player with a low FIP and high ERA will improve, while a low ERA and high FIP indicates a likely regression as more hits start falling. I've placed FIP next to ERA to make this comparison more obvious, but if it begins making the ERA lookup too hard, I may move it further right on the pitching tables.
I've also added FIP and K% to the Play Index Season Finder. Right now, I don't believe we will add xFIP given the inconsistency in batted ball data, but that could change.
Player with big gap in FIP and ERA: Ricky Nolasco.