There has been a fair amount of discussion about Danny "Gnar" Duffy this season, rightfully so. Among starters with at least 100 innings, Duffman ranks 5th in ERA, though among his peers (the top 30) in this ranking, he has one of the worst FIP values and the worst xFIP value.
We know the Royals have a good outfield defense. I won't bore you with more platitudes about the Royals outfield defense. We know the Royals have a pitching favorable home park. I won't bore you with more things about this. What I WILL bore you with is a short discussion of a recent article on FanGraphs as well as a deeper dive into a point made in the article.
I like this article. You should probably like this article. It goes beyond the simple ERA/FIP gap comparison and attempts to explain what's really going on. Blengino has access to data that the public does not, so we can glean insight otherwise unavailable to us when he writes stuff. The short answer, for those Saved You a Click fans, is that Duffy is really good at generating popups. Like stupid good. These are mostly free outs, which supplements his pedestrian strikeout rate. Duffy also kills fly ball production like [insert dictator here] oppressed [insert people here], regardless of the stadium and defense. He's talented in his own right.
Blengino, though, mentioned Jered Weaver as a comparison. Weaver is a guy who has beaten his peripherals fairly consistently due to his high popup rate, but he throws from the right side with funky mechanics and never had Duffy's velocity. Nevertheless, they compare fairly well. Below is a table showing each player's career stats as starters. Weaver has like 7 seasons on Duffy in terms of playing time, but bear with me.
Just about everything on that table is similar. Both players are middling strikeout guys who limit home runs and get a lot of fly balls. They both run low BABIPs and high LOB%. Duffy appears to be a left-handed Weaver, with one rather large exception: the walk rate. But, hey, most of Duffy's innings come from 2011 and 2014, which are several years apart for those with a calendar. How about their 2014 stats as starters?
The strikeout rate and walk rate are now very similar, but Duffy is showing better contact management skills with a lower BABIP and much lower homer rate. Obviously, the Royals' outfield defense helps Duffy out more than the Angels' outfield defense helps out Weaver, despite Trout's presence, but it really does look like Duffy and Weaver are very similar pitchers.
This offseason, I'm sure one of the topics will be if Duffy deserves an extension. While he is far outpitching his peripherals, he purportedly has the requisite skills to make some of that performance sustainable. Blengino claims that any drop in velocity for Duffy could erode his skills, though. Duffy is still young and building up his strength after returning from surgery, so maybe Duffy could hold his velocity for a few years. If he remains healthy, of course. Hopefully the shoulder thing is as minor as the team has advertised. The Royals need Duffy on the mound.