So What is FIP Anyway?

As discussed in the recent and most excellent For All the Dummies post, it appears that one reason some readers resist using statistics in evaluating baseball players is that the discussion of a particular stat often skips an explanation and goes straight to the conclusion.  The following is an attempt to provide a brief introduction and background to Fielding Independent Pitching or FIP, one stat that frequently gets discussed on Royals Review (and has generally gained acceptance by those who study baseball stats).  This post probably oversimplifies FIP a bit, but the main point here is to provide the general idea, not to start any debates, or link a bunch of research articles and studies (other than to note that current MLB consultant Tom Tango invented FIP and that I found this article helpful in explaining the basics of FIP).  For further reading, see devil_fingers epic post of links.

In short, what is FIP?  FIP is essentially a defense-neutral ERA that only considers three things demonstrably within a pitcher’s control – strikeouts, walks (plus HBP), and home runs allowed.  Defense – which plays a large part in deciding whether a batted ball is a hit – is intentionally removed from the equation, and thus corrects one of the main problems with ERA.

FIP calculates runs allowed based on Ks, BBs, and HRs and then to make it more accessible, expresses the runs allowed on the same scale as ERA (the calculation for FIP actually sets the league average FIP as the league average ERA for that year).  Thus, just like ERA, a 3.50 FIP is good, a 5.50 FIP is bad, and a 4.50 FIP is roughly average. 

Strikeouts, walks, and home runs also happen to be three things that correlate strongly for a pitcher from year to year (strikeouts and walks more so than home runs).  Because Ks, BBs, and HRs tend to repeat, so does FIP, making FIP a much better indicator for projecting a pitcher’s future performance than ERA.

What is the formula?  Not that you would ever need to use it personally, the formula is (HR*13+(BB+HBP-IBB)*3-K*2)/IP, plus a factor (usually around 3.20) to scale FIP to match league average ERA for a given year. 

Why does FIP use only Ks, BBs, and HRs, and not hits?  The answer to this question is another question:  what are the things actually within the pitcher’s control?  The four major things under a pitcher’s control are strikeouts, walks (plus hit batters), home runs, and the type of batted ball allowed (groundball, flyball, and line drive) that does not leave the park.  Obviously, defense is not one of them, and we know that whether a batted ball goes for a hit or an out depends in large part on the defense, so FIP intentionally removes hits (other than HRs) from the equation. 

OK, that makes sense to not include hits, but what about the type of batted ball allowed, which pitchers do have some control over?  This starts to get into the more advanced aspects, but the basic (and perhaps too simplistic) answer is that FIP generally assumes that a pitcher will have a league average batted ball profile (in other words, a pitcher will have league average groundball, flyball, and line drive rates) and thus allow a league average hit rate.  This removes a bit of accuracy for simplicity, but for many if not the majority of pitchers, the balls in play rates fall close enough to the league averages to not create a big difference one way or other.

An easy solution is to simply look at the pitcher’s batted ball rates (groundball rate, flyball rate, line drive rate) to determine if a pitcher is performing at, above, or below his FIP.  Other than to say that groundballs are generally good, flyballs are generally bad, and line drives are very bad, an evaluation of batted ball rates is probably best saved for a separate post.  An advanced version of FIP that does factor in batted ball data is tRA, which again, probably deserves its own post at some point.

So how do the Royals stack up?  As suggested in the comments, here is the list for the regulars in 2008. Please note that scoring was down last year throughout MLB, so the league average ERA and thus league average FIP was 4.32.  In short, Ramon Ramirez, Soria, Greinke, and Tejeda were very good last year, while Bannister, Yabuta, Gobble, and Peralta had trouble.