There is no doubting that Luis Avilan has had good results this season. With Eric O’Flaherty and Jonny Venters combining to throw 18 innings, Avilan stepped up and produced as the sole lefty for the majority of the season before Alex Wood’s call up and the acquisition of Scott Downs.
I was rather high on Avilan entering the year, especially since he was projected to be just the third lefty in the bullpen and was expected to essentially be a strict LOOGY. The injuries to the left-handers elevated his role and when Jordan Walden was injured earlier in the year, Avilan had to step up even more as his role was again expanded. So far he has posted a masterful 1.33 ERA, a mark lower than all but Craig Kimbrel’s (min. 10 IP with the team). The question I have is whether we should expect Avilan to be this good or whether it has been a 54.1 inning mirage.
I will preface my analysis by stating that relief pitchers are erratic. They can have great seasons or terrible seasons and not be throwing all that differently. They are thrown into such a small amount of work, even over the course of a full season, that the performances can and do often vary a significant amount year to year. For reference, check out Bill Petti’s post at FanGraphs from earlier this year on the correlation of relief pitcher metrics on an annual basis. In general, ground ball and fly ball rates do not alter a ton, but you see rather big differences start to pop up when you look at strikeout percentage, ERA, and home run per fly ball rate, to name a few.
Those are some of the areas I want to start at with Avilan. He has been a heavy ground ball pitcher, which is great since he has not been a strikeout guy at all this season. Relying on ground balls is a great way to limit extra base hit damage and having a guy like Andrelton Simmons playing the most important role in the infield certainly helps. For his career he has a 54.4% ground ball rate, which combines 36 innings last year and the 54.1 he has thrown this year. This season he is at 58.8%, about an 11% increase since last year. PITCHf/x also has him throwing his two-seamer 72.7% of the time compared to 38% of the time last year, which could be a reason for the big increase. Either he is throwing the two-seamer more often or his fastball in general is getting more break. For comparison, his four-seam percentage last year was 32.3% compared to 7.4% this year.
So it seems like he is throwing the two-seamer more often, or at least getting more two-seam type action on his fastballs, which would certainly help with ground balls but has not helped much with him missing bats. His swinging strike rate was 11.1% last year but he has dipped to 8.6% this year, and his strikeout rate has subsequently dropped from 23.2% to 14.1%, a significant and notable drop.
Combined with a decreased strikeout rate, Avilan has also seen his walk rate jump to 9.4%. To say that K%-BB% is not impressive is an understatement.
To me, the more I look at Avilan’s numbers, the more I see a mirage. Sure the increased ground balls should help suppress his BABIP a bit, but he currently has the second lowest mark in baseball (min 50 IP) at .186. The only pitcher with a lower BABIP is Tyler Clippard, but he has a 2.95 K/BB rate, so even if he starts allowing hits at a higher rate he should still be able to sustain a decent amount of success given his ability to punch batters out.
With Avilan, if hits start falling in, he goes from being one of the best bullpen arms on the roster to one of the worst almost instantaneously. His 1.50 K/BB rate is the 17th lowest in baseball (min. 50 IP). His strand rate is the 32nd best in baseball – while that initially sounds great coming from a reliever it is known to be a stat that players vary from then often regress back closer to league average, whether they are high or low on the spectrum. Here is a link to the FanGraphs library which further explains the metric.
Those signs all point even further to his performance being a mirage. To take one further step, he has allowed no home runs this year. While he is a ground ball pitcher, even ground ball pitchers eventually allow home runs. His 0.00 HR/FB ratio is obviously the best in the league, since you cannot get any better, but no other pitcher in the league has a 0.00 HR/FB rate other than Avilan (again, min. 50 IP).
My main point in this analysis is to explain that while Avilan’s performance has been good so far, the method with which he has received such good results is not a highly sustainable method. Could it continue for the rest of the season and into the post-season? Sure, baseball is a crazy sport. But if you are looking deeper than just his ERA, you start to see a number of glaring concerns that point to him not only being a guy who cannot sustain a 1.33 ERA over time, but to a guy who could be entirely unreliable in the bullpen. His xFIP and SIERA are both north of 4.00, and a reliever with that high of an ERA is not someone who often stays around a long time.
The concern I have is that the Braves will rely on Avilan in the post-season to produce at the level he has this season. He may certainly do so, considering how small of a sample playoff baseball allows, but if you are looking at a player’s true talent then he probably is not even the best left-hander in the bullpen to turn to. It is probably Scott Downs, who has a 1.64 ERA, 3.27 xFIP, 2.00 K/BB ratio, and a 3.10 SIERA.
This is not to say that Avilan is an awful reliever or that the Braves would be completely unwise to turn to him at all in the playoffs, but it is to say that I hope the team looks a bit deeper when evaluating when to use him this post-season. Hopefully Avilan’s strikeout numbers improve, as I would love for him to sustain his success over the course of this season and into next as the team evaluates whether to keep Eric O’Flaherty and/or Jonny Venters.