Why is Miguel Castro Breaking Out?

The leverage index showing in the table above is a measure of how much pressure the pitcher saw in the game. 1.00 = average pressure, higher is more pressure.  The next highest leverage index on the team is Scott McGough with 1.4.  WPA is win percentage added. This is often a good stat to reference when looking at reliever performance. Again the higher the better, and the only pitcher on the team with a better WPA than Castro is Zac Gallen.

Asked why he thought that Castro was pitching better, Strom gave a surprising answer. 

"His ability to tell me no on a daily basis that he’s not going to pitch. I told him that when we signed him. If you look back at his numbers with the Yankees and Baltimore and the Mets he was an abused pitcher quite a few times. He always took the ball, even when he wasn’t feeling right. I think that effected his effectiveness. "

The biggest improvement for Castro this year is better command and control. The velocity, movement, spin rates, etc, are all comparable to years past.  But his walk percentage is a career low 7.9%, compared to a 12.3% rate prior to 2023.  That's a whopping 36% drop in walk rate.  Strom explained why this is also tied to workload. 

"I think when a person is tired, I don’t think velocity is the first thing to go, I think command and control is the first thing to go. A guy can feel fatigued and still conjure up that feeling of getting enough velocity to get him out, but I think that command and being able to locate pitches is the biggest, I think that’s the thing that goes first."

Asked if he had to twist Castro's arm sometimes to get him to open up about how he's feeling, Strom said "A little bit, he often says he’s ready. I consult with our medical people, he’s often said he’s able to go and then there’s certain days we’ll say this guy will only pitch if we’re in a save situation."

When told about these conversations and the mention of Strom's name, Castro's face lit up into a huge smile, and he spoke very enthusiastically about his pitching coaches. 

"I would describe myself as someone who’s always tried to make myself physically and mentally ready and to be available. Yeah, in the previous years maybe I have pitched a little bit more innings than I should have. But I do try to maintain that open communication with Strom and with [Bullpen coach Mike Fetters] to let them know, have that open communication"

"Strom is a tremendous person. Since my arrival he’s been so appreciative of everything. He speaks everything really clearly. We talk about mechanics, we talk about stats. He’s definitely someone who since my arrival here has helped me out a ton."

Looking at the surface numbers one might look at the full season pace of 75 games and 70 innings and conclude the team has not really been successful in cutting back his workload. But that couldn't be further from the truth.  It's important to also look at the number of batters faced. Not all innings are created equal, and the lower walk rate means fewer batters faced per inning, and therefore fewer pitches thrown. Baseball reference provides some detailed numbers that give a much clearer picture of reliever workload beyond just games and innings

Looking at the table above, you can see several categories.  ">3o and <3o" are games where he had to get more or less than three outs.   "IPmult is the number of times he was asked to pitch multiple innings,  "Out/GR" is the number of outs recorded per game in relief. And "Pit/GR" is the number of pitches thrown per relief outing.  From all of these various measures it's clear that the D-backs have made a very conscious effort to change the way he's been used. This is a much smarter workload and so far the results have been outstanding.  

Whether that continues or not is hard to say of course. Relievers are notoriously volatile, and they are difficult to keep healthy. But the D-backs are doing everything they possibly can to get Castro through an entire season without overworking him.  

Don't expect Torey Lovullo to move away from the co-closer system any time soon. He spoke about how this system keeps him more engaged and challenges him to think through the usage more than he has in the past.  By using this system it gives him the opportunity not only to matchup, but also keep guys fresher.  He's clearly figuring it out. For the season the D-backs have a 4.02 bullpen ERA, ranking 16th in MLB. But since May 1st that number is 3.44 and ranks 10th. 

If you have a few moments, you can also listen to Strom and Castro on the sound cloud below. Well worth the listen.