Danny Duffy’s Got the Stuffy

Throughout his career, Danny Duffy has shuffled between the Royals starting rotation and their bullpen. Let’s compare his underlying skills in each role:

Pitchers generally perform better as a reliever than as a starter, but this is quite a stark difference. Check out that strikeout rate surge when moving to the bullpen! And his walk rate has been better as well. His SwStk% almost doubles to elite levels. The only thing Duffy does better as a starter is induce pop-ups. Thanks to all those extra near automatic outs and increased fly ball rate, his BABIP is a touch lower as a starter. But it’s not enough to make much of a difference on his results — both his ERA and SIERA are nearly and exactly two full runs better as a reliever, respectively.

Let’s check out his pitch mix in each role to determine what, if anything, he has done differently:

As a reliever, he throws his fastball more frequently, and as is typically the case, it comes in faster than it had when he starts. A two mile per hour jump is certainly above average for pitchers moving from the rotation to the bullpen, but not outrageously so. That said, averaging over 95 mph as a lefty is pretty darn good. Everything else goes two to three miles per hour faster as a reliever, but as a starter, he used his curve and changeup more often, at the expense of his fastball.

This season, Duffy opened the season in the bullpen, but injuries opened up several rotation slots, which gave Duffy the opportunity to move back in. He’s only made five starts so far, spanning 25 innings, but he has been pretty spectacular. Let’s look at the underlying skills first over those five starts:

That’s a 28/2 K/BB ratio. He’s become an extreme fly ball pitcher, which ain’t so bad in Kauffman Stadium, a park that heavily suppresses homers. Not to mention pitching in front of a fantastic outfield defense. That increased fly ball tendency has likely led to an inflated IFFB%, which means even more easy outs. He’s basically become his rotationmate Chris Young in that respect, but with far better strikeout ability. Check out that SwStk%! That’s a tick higher than his already elite mark as a reliever.

Now for some of the why. Let’s check out the pitch mix:

What should immediately jump out to you is what hasn’t happened. That’s a decline in velocity after moving back into the rotation. If you recall, throughout his career (my stats included this year), his fastball velocity as a starter was 93.6 mph, versus 95.6 as a reliever. This year, he has nearly maintained his relief velocity as a starter. That’s a big deal and could do wonders if he could sustain that increase.

Furthermore, he has upped the usage of his changeup and it’s generating swings and misses like never before. His breaking ball remains whifftastic, and the SwStk% on his fastball for the entire season is double his career mark at an elite 17.6%. There’s no way it stays that high, but it means he’s currently throwing three significantly above averages pitches from a whiff perspective.

Amazingly, if you check the SwStk% leaderboard and use a 40 inning minimum, Duffy finds himself at the top, and by a respectable margin. His 16.6% SwStk%, is well ahead of Jose Fernandez’s 15.2% mark in second place.

In addition to all the swings and misses Duffy has induced, he’s also doing something else he had only been mediocre at previously — throwing strikes, lots of them. His strike percentage has skyrocketed and would actually lead baseball among starters if he qualified for the leaderboard. If you include all pitchers without a minimum, he ranks 17th out of 548.

So let’s sum things up. Danny Duffy is throwing as hard as a starter as he had as a reliever, generating a league leading rate of swings and misses and displaying pinpoint control by becoming a strike throwing machine, all the while allowing lots of fly balls in a park and on a team where that may actually be preferred, and generating many easy outs via the pop-up.

If Duffy is somehow still available in your league, regardless of format and size, pick him up immediately.