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Danny Duffy’s Dynamic Fastball


Danny Duffy is a talented pitcher. We’ve known that much for several years now. What we were less sure about was whether Duffy would be able to harness his talent to become the kind of frontline starter the Royals were hoping for. The stuff has always been there, but the results didn’t always match up.

Well, the results are starting to match the stuff.

After his dominating performance against the White Sox, Duffy has thrown 54 innings this year with a 2.83 ERA. His FIP (3.88) and xFIP (4.57) suggest some regression is coming, but I don’t think it will be nearly that much, because of the way Duffy has been successful. He’s generating a ton of weak contact, and while he may allow more than a .195 opponent batting average, his stuff tends to keep batters from squaring him up very often.

His fastball, in particular, has befuddled opponent bats. Here are his batting lines allowed on his fastball from 2014, and from before this season:

2011-2013: .272/.383/.432
2014: .171/.261/.260

In other words, hitters turn into Mike Moustakas with less power when Duffy throws his fastball.

That kind of excellence has resulted in Duffy’s fastball being as valuable as any other fastball in baseball. Using Pitchf/x pitch values, only Johnny Cueto and Phil Hughes have better fastballs this season, among pitchers with at least 40 innings. Those values take every pitch into account, including those not put in play, meaning throwing strikes is very helpful. This season, Duffy’s throwing his fastball for strikes.

In previous seasons, Duffy threw his fastball in the zone around 56% of the time. In 2014, that has gone up to 58.8%. That’s even more important considering he’s thrown first-pitch fastballs over two-thirds of the time this season. He’s throwing a lot of fastballs early, and they’re helping him get ahead early, as shown by his first-pitch strike rate of 58.5%, well above his career average of 53.7%. Getting ahead of hitters is always a good thing.

Now back to the fastball. As I mentioned, guys aren’t making great contact against it this year, and you can see that just by looking at the batting line above. But there’s one more number I find fascinating that also helps illustrate that pitch’s greatness. This season, Duffy’s fastball has generated an infield fly ball rate of 33.3%. That means that one out of every three fly balls doesn’t even leave the infield. I find that statistic even more impressive since Duffy relies so heavily on his fastball (only two pitchers in baseball throw their fastball more frequently), and since he has a fly ball rate of 51% with that pitch, meaning  this isn’t just 3 popups on 9 fly balls.

And this is something Duffy’s done in the past, which suggests it’s not a fluke. His career IFFB% on his fastball is 28.3%, and that’s only dragged down by a tiny sample in 2013. In 2011 and 2012, that IFFB% was 27.4% and 34.8%, respectively. Duffy’s shown the ability to generate weak contact with his fastball before, but this year, he’s not giving up as much hard contact to counteract it. His line drive rate on fastballs is at 20%, which is below his average of 23%. Add that all together, and you can see why Duffy has been so great this season.

All of this isn’t to say Duffy is now an ace, or anything like that. He isn’t getting as many strikeouts as you’d like to see, and despite his start against the hacktastic White Sox, he’s still walking a few more batters than you’d prefer. However, he is throwing more pitches in the strike zone, and because of the quality of his stuff, hitters haven’t been able to do much with it.

He’s getting the kind of results you’d expect to see from a pitcher of his caliber, even if he’s doing it in a slightly different way. If opponents start to make better contact, Duffy may need to adjust some, but until that point, the Royals are probably pretty happy having him rely on his outstanding fastball.

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  • jessanders

    It’s certainly better than having Davis and Mendoza in the rotation. You never felt confident with those guys, but Ventura and Duffy make me feel much more confident than they ever did.

    Vargas is ridiculous and I don’t understand how he’s doing it, but he is. Good on him.

    Guthrie still makes me nervous everytime he pitches, but he’s a back of the rotation starter, so it’s to be expected.

    The point is, Duffy is turning into a mid-rotation guy with flashes of #2 stuff. We now have a guy who flashes Ace stuff and is clearly a #2/#1 pitcher in Ventura, and Duffy as home-grown pitching. If we can get one of Manea and Zimmer to turn into a true #1 starter, then we’ll have the front end of our rotation sewn up for years to come.