Way out in the National League West, the much-mocked Barry Zito and the much-debated Trevor Cahill are both off to good starts. Both players got their starts with the Oakland As before moving the to National League. Of more interest is that both players have, at different times, been held up as examples of pitchers for whom DIPS stats like FIP are inadequate. Without getting into lengthy discussions of each pitcher or the whole debate about DIPS (of which FIP is just one variety), let’s take a look at Zito and Cahill’s early-season performances with a glance at their past performances and see if there is anything of interest.
Read the links above for general introductions to the general principles behind DIPS and FIP, I will not re-run it here. I do think that DIPS and FIP are somewhat misnamed in their emphasis on “defense” and “fielding,” since the random variation for pitchers on balls in play (or, put differently, the relative dearth of variation in BABIP true talent for pitchers compared to hitters) is probably the bigger issue.
Terminological quibbles aside, let me very briefly give my (probably not very unusual) take on the issue of FIP versus ERA (or RA). I do not think that FIP (or other, more sophisticated DIPS stats like SIERA, I am using FIP as a stand-in for DIPS because of its simplicity) is the “perfect” pitching stat. Hopefully current and future research will lead us to something better. I simply think it is usually more helpful than ERA. However, I do not even think that it is necessarily always a better indicator of a pitcher’s skill than ERA for every pitcher. After a very large sample, ERA/RA is better for individuals. Perhaps I can summarize my own thoughts this way: In a limited sample (less than three seasons), FIP is better for most pitchers.
[I've probably already distracted from what I really want to discuss, but I wanted to at least get that out there. And I'll probably regret putting it the way I did. Those are the breaks, I guess.]
Over more than 2200 career innings, Barry Zito’s career FIP is 4.32 (4.72 xFIP), but his career ERA is 3.89. It seems that he has had (at least at some points) the ability to “outpitch” his DIPS metrics. This season seems to be a case in point, as he has a 1.67 ERA versus a 4.01 FIP and 4.65 xFIP. Some have even speculated that Zito has fixed the problems of prior seasons. Of course, as Craig Calcaterra points out, the same thing was written during prior hot starts by Zito that cooled off rather quickly (as should have been expected). Even if we ignore the most important issue — the small sample of Zito’s 2012 performance versus most recent years — the chance that he keeps this up is small. While his walk rate is good, his strikeout rate is also the lowest of his career so far. Zito is doing his usual flyball thing, but a .188 BABIP just is not going to happen on the year, nor is Zito going to continue to strand more than 90% of the baserunners he puts on.
As has been pointed out, Zito has had recent starts like this before. But even if one thinks he still has the ability to out-perform his DIPS metrics (he didn’t do so in 2011, and he did just barely in 2010), his ERA has ended up regressing back towards them during the season. Given that his most indicative peripherals are not all that impressive to begin with, there is not really much to hope for here.
Cahill presents a case that is similar in some respects, but is also different in interesting ways. Perhaps the most obvious difference between Cahill in Zito is that while Zito (at his best) has kept his BABIP down by way of lots of flyballs, whereas Cahill has done so by way of a pronounced groundball tendency. Cahill already started outperforming his FIP in his 2009 rookie debut, but a 4.63 ERA is nothing to get too excited about, especially with Oakland as his home park. In 2010, however, he was floated as a dark horse Cy Young candidate on the basis of a 2.97 ERA. Given that his 2010 FIP was 4.19, he was held up by some as another “counterexample” to DIPS.
Cahill’s ERA was not as good in 2011, although he did significantly up his strikeout rate. While getting to face the pitcher in the National League may have helped his overall 2012 numbers so far, it is also worth remembering that his new home park is one of the most hitter-friendly in baseball. With uthe sual early-season qualifications noted, his 3.13 ERA so far in 2012 is very impressive. If Cahill can keep getting enough groundballs keep that up despite a having strikeout and walk rates worse than average, then the Diamondbacks may have something very exciting on their hands. (Small sample, etc.)
What is particularly interesting about Cahill as opposed to Zito, however, is that his 3.13 ERA this year is not all that much better than his 3.35 FIP (3.55 xFIP). This is not a new development — his 4.16 ERA was almost exactly the “same” (actually slightly worse) as his 4.10 FIP in 2011 (3.90 xFIP). What attracted my attention in Cahill’s case this: after 2010, some DIPS-skeptics pointed to Cahill as a pitcher who was, despite what FIP and other metrics seemed to indicate, a very good pitcher. In 2012, he is bearing out the “very good” part, but contrary to the assumption of DIPS-doubters, he is not outperforming his FIP all that much so far, and did not in 2011 either. Cahill might be an example of a good pitcher, but as time goes on, we have seen that his ERA is regressing towards his FIP.
I have no systematic thesis or conclusion here, just the observations above. Both Zito and Cahill have, in their own ways, outperformed what FIP would lead us to expect in the past. However, it hardly means we should abandon FIP or other DIPS metrics generally or even in the case of these two pitchers. Zito has had hot ERA starts before, and usually ends up regressing towards his FIP. And while Cahil may be pitching better than what we might have expected after 2009, he, too, is more and more getting ERA results close to his FIP. FIP is far from perfect, but it still turns out to have been informative for supposed “exceptions” like Zito and Cahill.