By the Numbers: The single move the Twins need to make right now to fix their bullpen.

It is a very young season, but the Twins' bullpen, albeit new, did not look as improved as it should for a team that aspires to contend in the post-season before the season started, and it has started to look so on the field so far.   The Twins' pen ranks 18th in the MLB in ERA, 22nd in the MLB in FIP, and 23rd in K-BB%.

Using three modern measurements, it is fairly clear who are the players who are lagging in the pen.  Here are the Twins' relievers' rankings by:

Win Probability Added (WPA) that is probably the single best overall measurement of reliever performance:

Addison Reed 0.30
Taylor Rogers 0.19
Gabriel Moya 0.02
Tyler Kinley 0.00

Ryan Pressly -0.03
Fernando Rodney -0.04
Trevor Hildenberger -0.07
Zach Duke -0.11

A couple more measurements that refine WPA:

RE24 or Situational Run Expectancy.  For more information look here, but in one sentence (from that link,) pitchers with positive numbers are preventing more runs than average given the situations in which they have been placed.

Taylor Rogers 2.69
Addison Reed 2.61
Ryan Pressly 1.48
Fernando Rodney 1.00

Tyler Kinley -0.45
Gabriel Moya -0.67
Zach Duke -1.25
Trevor Hildenberger -2.34

and Fangraphs Clutch. which is (WPA / pLI) – WPA/LI (where LI is a particular player's leverage index and pLI his average leverage index) which measures how much better or worse a player does in high leverage situations than he would have done in a context neutral environment.

Fernando Rodney 0.10
Gabriel Moya 0.10
Zach Duke 0.03
Adisson Reed 0.01
Taylor Rogers 0.01

Tyler Kinley -0.05
Trevor Hildenberger -0.16
Ryan Pressly -0.17

What do the data show?  Clearly there is a single pitcher who lags the rest in all categories, Trevor Hildenberger.  One can argue that Zach Duke does so as well, which is a correct statement; however he does not in high leverage situations, as shown in the Clutch measure.  The Twins should start using him more in high leverage situations.  On the other hand, Hildenberger really has ho business being with the Twins right now and since he has an option, he should be the one demoted for a fifth starter, when the Twins need one, or even before they need one.

Who should that fifth starter be?  Fernando Romero.  About time the Twins get the guy with the highest potential, who has proven that he is ready in Spring Training, playing in games that matter.  In the bigs.

Optioning Hildenberger and recalling Romero will go long ways to fixing the Twins' pen (and rotation) as well...

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