Danny Duffy's fastball

Danny Duffy was a bit of a revelation this year. I wasn't sure what to expect from him. Were you expecting anything good? What we got was pretty good. Duffy finished with 2.2 fWAR in 149.1 innings, 31 total games, and 25 starts. Had he lasted the whole season as a starter, he could have been closer to a 3 fWAR player, assuming lots of things that I probably can't assume like health, effectiveness, blah blah blah.

Duffy seems to be a bit of a lightning rod for discussion. Many see his shiny, rainbow-clad 2.53 ERA and say, "Extend him". Many of you see his 4.42 xFIP and say, "Regress him". Neither opinion is necessarily wrong, but let's move past those numbers into some different numbers that might be illustrative why the large difference occurred between his actual runs allowed and his peripherals.

I would submit that luck and defense and ballpark played a part. Guys don't allow a .239 BABIP without some luck. The 77.2% LOB rate falls into the same luck category. Duffy had only a 35.8% GB rate, so he's definitely a fly ball pitcher, and we've seen what the Royals' defense does to fly balls. So, obviously, he was helped by factors outside his control. He was also helped by factors within his control.

FanGraphs has linear weight rankings of pitches. If you're unfamiliar, linear weights assign each event (strike, ball, single, etc) a run value. Over the season, these add up. A score of 0 is average. In addition, since pitchers throw pitches in different frequencies, FanGraphs also adjusts each number per 100 pitches to put each pitch on a level playing field. Unfortunately, or fortunately, depending on your point of view, FanGraphs takes in two sources of data for these: Baseball Info Solutions and the raw PitchF/X data. I'll show you below Duffy's rankings for both the total value and the per 100 pitch value by each data source among pitchers with at least 100 innings pitched in 2014.

Duffy's fastball was among the best. Even though it was outside the top 10, pretty much all pitchers throw a fastball, so there is a large number of pitchers who qualified for this ranking (149 to be exact).

So what makes Duffy's fastball different? For one, how he uses it. The general pitching philosophy is "keep the ball down", yes? Duffy does that less than most. This article here shows that the rate of pitches thrown down has increased slightly while the rate of pitches thrown up has decreased slightly (all within the strike zone, not considering pitches outside the strike zone. A significant caveat). It also appears that the actual rate of pitches thrown up in the zone is below 10%, but it's hard to tell. Duffy, in contrast, threw about 14% of his total pitches in the upper third of the strike zone. Below is a zone profile of where Duffy located his fastball in 2014.

While Duffy might throw up more than most pitchers, he still stays relatively unpredictable with the fastball. He'll stay away against lefties, but he's not afraid to bust righties in. He'll change eye levels with the pitch.

Another aspect of Duffy's fastball that helps is closely tied in with the "keep the ball down" philosophy. Most pitchers add significant run and/or sink to help keep the ball down and generate ground balls. Duffy says no to that approach; Duffy's fastball "rises". By that I mean that compared to gravity controlling the sink of the pitch, Duffy's fastball sinks less than expected. This has helped generate Duffy's lovely infield fly ball rate, which ranked 4th among those pitchers who threw at least 100 innings in 2014.

And there it is. Duffy's popup rate. While Duffy had a mediocre-to-not-great strikeout rate, he made up for it with popups. This is probably to help decrease his pitch count to stay in games longer. Duffy made it to 6+ innings quite a bit this year. This also helped the gap between his ERA and his peripherals. Since the peripherals don't take popups into account, which are almost equivalent to strikeouts, popups will show up in the ERA but not the peripherals. The Royals will need this skill in 2015 to make their repeat run and win the World Series. Let's hope Duffy can repeat it.