Selling Danny Duffy

As you may recall, I jumped onto the Danny Duffy bandwagon rather early on, diving into his ability to sustain his relief velocity as a starter through his fifth start of the season. Since those first five starts, he has continued to pitch spectacularly, posting a 2.43 ERA (3.43 SIERA) and 21.5% K-BB%. But the good times eventually come to an end. And I think Duffy’s value has peaked and is in danger of experiencing a sharp decline.

Let’s break up his performance as a starter into several different periods. Though this might be a controversial decision, I decided to exclude his absolutely dominant August 1st game against the Rays in which he racked up 16 strikeouts and allowed just one hit. The game was such an outlier for all his underlying peripherals that it would have distorted his overall line during the time period. So out it went.

As a result, I broke up Duffy’s starts into three periods — before his velocity loss and then after his velocity loss, with the Rays game separating the post-velocity loss period into two (five games and then three games started).

Let’s look at the process first:

Immediately, we see the loss of velocity. The most exciting thing about Duffy was that he had managed to sustain the vast majority of his fastball velocity as a reliever while starting. But that all changed in his 10th start as his velocity dropped and hasn’t recovered. This chart is ugly:

Sure, we didn’t expect him to maintain his velocity as a reliever. But initially, at least over his first nine starts, he did. And that’s what made him so exciting. You see that for the most part, aside from the odd middle period, he’s been an extreme fly ball pitcher. If any pitcher ever hopes to succeed as an extreme fly baller, then doing so in Kansas City is the best possible place to do so. Unfortunately, his ability to induce pop-ups vanished over his last three starts. The sample size is tiny, of course, so perhaps this is just a fluke and not a sign of impending doom.

But hey, he’s still pitching well, right? Let’s check in on the rest of his metrics:

For a pitcher who throws in the mid-to-high 90s and has posted a high strikeout rate, it’s pretty crazy to see those inflated Hard% marks over each period. But let’s move off that metric and focus on a more telling one — SwStk%. Duffy was absurd over his first nine starts, making batters swing and miss at an elite clip. Since his velocity has declined, he has been just ordinary and his strikeout rate has plummeted. The one sliver of good news is that he has been able to sustain his significant control gains throughout.

To the far right, you will notice that his SIERA has been on the rise. However, he’s relying on some magic to keep his ERA from feeling the effects of his skills deterioration. Over his last three starts, his SIERA is a weak 4.44, but he has posted a 1.54 ERA (just four runs allowed in 23.1 innings) thanks to a .203 BABIP and 92.6% LOB% (and to a slightly lesser extent, the suppressed 5.9% HR/FB rate). That low BABIP has come despite a very high Hard% and a low IFFB%. And of course, he has stranded nearly every runner that has reached base.

Duffy pitched 144.2 innings last year and is at 132 already this season. He threw 155.1 innings in 2014 as well, so he shouldn’t be running out of steam just yet. But it sure seems like that’s what’s happening.

I’m not going to predict a collapse. He still possesses good stuff, even with a tick less velocity, and he’s showing no signs of backtracking from his improvement in control. But this is a guy with a 2.73 ERA and over a strikeout an inning whose perceived value may be sky high at the moment, especially in keeper leagues as he’s just 27 years old. If you’re risk averse or just curious, I say now is the time to shop him around and maximize your return.