Danny Duffy could be the next Wade Davis

On Sunday afternoon, Danny Duffy was asked to relieve Kris Medlen against the Detroit Tigers. Duffy had been disappointing as a starter following his breakout 2014 season--he accumulated a 4.35 ERA as a starter, making only 24 starts and lasting barely 5.1 innings per start. Duffy was not terrible as a starter this year, but he did not perform to the expectations of Dayton Moore and Ned Yost (alongside Yordano Ventura, who is in the mire of a similarly disappointing season).

Duffy's performance on Sunday was markedly different from most of his outings as a starter. Duffy pitched four innings, notching six strikeouts while walking none and allowing two hits. He looked like a truly special pitcher; Duffy was getting a head of hitters, keeping them off balance with an overpowering fastball and biting offspeed and breaking pitches.

Yost's reason for moving Duffy to the bullpen was purely geared for the postseason. The Royals bullpen has been surprisingly porous of late, especially with the catastrophic meltdown of closer Greg Holland. Moving Duffy to the bullpen now gets him time to acclimate to such a role as well as shoring up the bullpen, for Duffy was going to be the odd man out anyway with the four-man playoff rotation. Since Duffy's return from Tommy John surgery in 2013, he has made 54 starts, putting up a 3.25 ERA and a 4.12 FIP. Duffy has basically been an average pitcher for his career, and though that sounds like a negative, average pitchers have significant value.

But Duffy's Sunday performance, alongside his six bullpen appearances in 2014 wherein he struck out 11.9 batters per nine innings, suggests something interesting: Duffy could be an extremely effective reliever if Kansas City shifted him to be one. Indeed, I'll go as far to say that Duffy could be the next Wade Davis, which is a converted starter who makes a name for himself as a shutdown, late-innings reliever.

Here's why I think this could be the case.

Danny Duffy, the Starter

Any pitcher's job is to prevent runs from scoring. This much is obvious to anybody who knows what a baseball is. But starters have a particular set of requirements to which relievers do not adhere. Namely,

• Starters pitch efficiently to go deep into games,
• Starters get batters out multiple times as the order comes back around, and
• Starters get both left and right handed hitters out

Starters should prevent runs and eat innings, and good starters checkmark each of the three previous points. A starter who is unable to pitch efficiently will reach a pitch count limit and force a manager to go to his bullpen early, a starter who cannot get through the lineup a second or third time must also be removed for the bullpen early, and a starter who struggles with a certain handed hitters will be punished by pinch-hitters or a left/right skewed lineup.

Duffy is not particularly effective at any of those. Duffy walks a higher than average amount of people and is fouled off an above average amount of time; this combined with often nibbling at the plate and an inability to finish batters means that his efficiency is very poor. For his career, he averages 5.1 innings pitched. For comparison, his teammate Johnny Cueto averages about 6.1 innings per game.

Duffy also struggles when going through the order more than two times. In his first and second times through the lineup, Duffy allows an OPS of .696 and .693, respectively. In the third time through the order, Duffy allows an OPS of .857.

Finally, Duffy is significantly better at getting lefties out than righties. Against lefties, Duffy's OPS against is a meager .596. Against righties, that number balloons to .772. Certain types of pitches are better than others at getting opposite handed hitters out. The changeup is king in this regard, but curveballs are also good. Duffy doesn't really have a good changeup--hitters hit 21% better than league average against that pitch. He does have one, which is better than a lot of Royals failed starters over the years, and that combined with an excellent curveball is why he's been able to stick as a starter.

But Duffy as a reliever would be something else.

Danny Duffy, the Reliever

Relievers don't operate under the same constraints as starters. This is because

• Relievers don't need to worry about pitch efficiency
• Relievers only deal with each batter they face one time
• Relievers can utilize max-effort delivery and their full arsenal to neutralize right/left handed weaknesses

Relievers do not have to worry about facing hitters more than once. They are only worried about getting their 3-6 hitters out by any means necessary. This means no saving pitches and no holding back velocity for stamina's sake.

Wade Davis, Luke Hochevar, and Andrew Miller are all starters who converted to the bullpen in their careers. Each player saw a significant rise in effectiveness. Part of that is due to their jump in velocity; their average fastball velocity rose between two to four MPH. There is a big difference between a fastball that averages 91-93 and 94-96.

None of those players had particularly stellar fastballs as starters, though, which is something that Duffy does have. Among the 103 starting pitchers this year who match Duffy's innings pitched total, Duffy ranks in the top quarter at 24th with an average fastball of 93.5 MPH.

But Duffy is a rare breed--he's a lefty. Only three of the top 24 fastballs come from the arm of a southpaw. Those three players? David Price, Clayton Kershaw, Danny Duffy. Duffy's fastball velocity among lefty starters is truly elite. If Duffy's fastball gains two MPH on average in the move to relieving, Duffy would rank 25th among relievers this year. If Duffy's fastball gains four MPH on average, he would rank 4th.

The reality, though, is probably somewhere in between. If Duffy's new average fastball speed is 96 MPH, only 18 relievers with at least 30 innings pitched this year could match it. Those names include Aroldis Chapman, Craig Kimbrel, Dellin Betances, Kelvin Herrera, and Trevor Rosenthal. Not even Wade 'Cyborg' Davis makes that list.

Maybe the best thing about Duffy moving to the bullpen would be a focused arsenal of pitches. When Davis made the move to the bullpen, he ditched his slider, two-seam fastball, and changeup completely. Likewise, Duffy could shed his changeup and focus on a fastball/curveball combination. A two-pitch arsenal works for Davis, and it worked for Greg Holland until yes fading arm betrayed him. Duffy's curveball is good already; batters hit 30% worse than league average against it for Duffy's career.

Should the Royals move Duffy to the 'pen for good?

This is the key question, but the answer is not clear-cut. Unlike Davis, Hochevar, and Miller, Duffy is a useful starter already. A move to the bullpen would only be to maximize Duffy's performance as a pitcher. Duffy would almost certainly be a better reliever than starter.

But moving Duffy to the bullpen wouldn't necessarily maximize his value. Averaging Baseball Reference and Fangraphs pitching WAR, Duffy has provided 4.4 wins above replacement in 302 innings, or about 2.6 WAR per season (of 180 innings pitched). No reliever has provided 2.6 wins worth of fWAR this year.

The question, then, is what Duffy's performance will be going forward. If his true talent level as a starter is less than 2.6 wins per season, then maybe a move to relief is a good thing. On the other hand, his actual success as a reliever is unknown. He'll probably be good, but nobody knows if he will be good.

If nothing else, his move to the bullpen this fall will give us more information about Dan the Reliever. So far, so good. The awesome Duffy is the best Duffy.