Small Sample Size Fun: 30 Day Surprise xFIP Leaders

I tend to ignore small sample size trends and usually throw up a little in my mouth when I read that so and so pitcher is “hot”. But sometimes, these positive trends are actually the result of quiet mechanical changes or the so-called light bulb suddenly going off. Of course, it is very difficult to pick out which pitchers are experiencing a real change in skill and which are just having a good run. Anyhow, I decided to have some fun and sort by xFIP over the last 30 days and peruse the first page of the leaderboard. Some of the more surprising names I found were…

Jonathon Niese | 2.87 xFIP

Niese is pitcher a bit better than last year, but he has a solid skills foundation with an above average GB% and K/9 and good control. In the last month, he has bumped all his skills up a bit, but I have a hard time believing he could sustain a strikeout rate above 8.0. With a below average SwStk%, I think his season K/9 rate more accurately reflects his talent right now. I think he should easily outperform his rest of season ZiPS projection calling for a 4.25 ERA, but I would expect him to post an ERA similar to where he currently sits, rather than a skills surge pushing his ERA anywhere near his last month’s xFIP.

Jason Marquis | 3.20 xFIP

Marquis has generated such a surprising xFIP by inducing a fantastic 60% ground ball rate, and bumping his strikeout rate to its best level since 2004. Unfortunately, none of this looks sustainable. He has typically induced grounders at a rate of around 50%-55%, and the improved control he has shown is not supported by his F-Strike%. We obviously have enough of a history here and at age 32, it is highly unlikely that this last month carries any significance for Marquis’ expected skill level going forward.

Juan Nicasio | 3.35 xFIP

All of Nicasio’s Major League starts have occurred over the last 30 days, so this encompasses his entire performance. A .352 BABIP has killed him, though a 25% line drive rate is to blame, whether the result of bad luck or poor pitching. Given his strong minor league track record, in terms of strikeouts and walks, and 94 mile per hour average fastball, I would normally be rather optimistic about Nicasio’s chances to see his luck turn around. Unfortunately, his minor league BABIP has never dropped below .315, and though we know that defense is obviously worse in the minors, this is still a red flag. This is in addition to the fact that Nicasio has never pitched an inning at Triple-A. He seems to have the stuff and a nice skills foundation to work from, but it looks like he could use some more time in the minor league level.

Well so much for that experiment. With the hope of uncovering a future breakout, all I found were pitchers I believe will pitch just as expected, essentially putting no weight on their last 30 days performance.