2017 Fantasy Baseball draft strategy: Dip in velocity a concern for Danny Duffy?

Danny Duffy's results haven't been bad, but his velocity is down pretty significantly in the spring. Is it anything to worry about?

There’s never been much of a question as to whether Danny Duffy could be an ace. If you’re looking to build an ace, you can start worse places than a 6-foot-2 lefty with mid-90’s velocity, and if you held onto your Duffy stock over the roller coaster ride that has been his professional career, you finally started to see returns on that investment in 2016.

An early-season stint in the bullpen helped Duffy become more comfortable pitching out of the stretch, and he returned to the rotation midseason with more velocity than ever before. He was largely able to maintain that velocity in the rotation, and ultimately ended up averaging 95.5 MPH with his fastball per BrooksBaseball.net, a full tick up from his career average.

So it shouldn’t come as much of a surprise that Duffy also pitched better than ever before. His ERA clocked in at 3.51 and if that number wasn’t quite as shiny as his 2014 mark, it was backed up by much more impressive peripherals. Duffy raised his strikeout rate to 25.7 percent while lowering his walk rate to 5.8 percent and though troubles keeping the ball in the yard persisted, he still very much showed the makings of an ace.

And he has mostly maintained those improvements so far this spring. Pitching for Team USA in the World Baseball Classic, Duffy has allowed just one earned run on eight hits and a walk over eight innings, while striking out eight. That his second start came against a dominant Dominican Republic lineup that might be better than any in the majors only makes his success look even more impressive.

However, there is one thing to keep an eye on here, and it’s the radar gun. If Duffy’s improvement was fueled at least in part by the newfound ticks he found on his fastball, a dip in velocity would be reason for concern. After averaging 95.5 MPH with his fastball last season, Duffy is down to 93.2 in the two starts tracked at BrooksBaseball.net.

Typically, you expect velocity to be down for any given starting pitcher earlier in the season with BaseballProspectus.com finding a few years back that average fastball velocity is at its lowest in April, before steadily rising to a peak in the mid-summer months. Things tend to dip back down in September, which all makes intuitive sense. It takes a while for a pitcher to get warmed, and it’s harder to sustain peak velocity nearly 200 innings into a season.

Still, this is a pretty big dip we’re seeing from Duffy. Not only is he more than 2 MPH south of his season-long average from 2016, he is even 2.5 MPH down from last March. In fact, the 93.4 MPH he averaged Saturday against the Dominican Republic would have been his lowest for any start. According to that same BaseballProspectus.com piece, the change in velocity tends to stick from spring to regular season. Barring a change in his next few appearances, be they in the WBC or spring with the Royals, it seems likely Duffy will enter the 2017 season without some of the heat on his fastball.

You might be asking yourself, “so what?” Fair! Duffy has managed to pitch very well, even against tough competition, so his diminished velocity may not be much of an issue. However, velocity correlates well with strikeout rate and swinging strikes, and that was certainly the case for Duffy in 2016, as the following chart shows:

2016 Fastball Results by Velocity
No.	Velo	% of FB	WHIFF%	BA	ISO	Exit Velocity
37	< 92 MPH	2.3%	2.7%	0.556	0.667	98.5
110	92-93 MPH	6.8%	5.5%	0.417	0.333	96.9
291	93-94 MPH	18.0%	6.5%	0.250	0.236	92.5
413	94-95 MPH	25.5%	9.0%	0.243	0.175	92.3
432	95-96 MPH	26.7%	14.1%	0.277	0.158	88.4
250	96-97 MPH	15.5%	18.0%	0.300	0.333	93.3
85	> 97 MPH	5.3%	15.3%	0.045	0.000	84.3

This isn’t exactly groundbreaking stuff, but there’s value in checking our assumptions against the data. And in this instance, they line up just as you would expect. Duffy’s results were quite a bit worse in the lower reaches of his velocity range, and for the most part, they improved as his velocity climbed higher. It doesn’t mean Duffy can’t be effective working in the 93-94 range, but he wasn’t last season. 

I’m still not betting against Duffy yet. There is time for him to find his velocity, and it wouldn’t be a surprise to see him climb back up to the mid-90’s before the end of the spring. That would safely put him in range of where he was last season, and would quell most of these concerns.

But if he is still in the 92-93 range by the time the regular season comes around, there will be reason to be concerned. Velocity isn’t everything, but it clearly played a part in Duffy’s breakout in 2016, and if he doesn’t have quite the same heat, expectations likely would need to be downgraded.

How much? That’s harder to say. Duffy doesn’t have a long track record to fall back on and, in 2016 we saw his effectiveness dip in the second half. Duffy’s average velocity fell from 95.6 MPH in his first 19 starts to 94.7 MPH in his final seven, during which time his ERA jumped to 6.37, and he allowed 12 homers in 41 innings of work.

Fatigue certainly played a role in Duffy’s late-season swoon, but he doesn’t necessarily have that same excuse right now. Duffy’s diminished velocity hasn’t been an issue for him yet in the spring, but for someone with such a limited track record -- who is still being drafted as a No. 2 SP in the top-100 overall -- it’s a warning sign that we shouldn’t be too quick to ignore.