Why Keeping Mason Miller in the Bullpen is Padres' Best Path Forward

Mason Miller was brought over at the 2025 trade deadline to help the San Diego Padres make a push for the World Series. While that pursuit ended up coming up short, he showed in the playoffs why the Padres emptied out the farm for him, tying the MLB postseason record for striking out eight consecutive batters while giving up no runs in both of his appearances. 

Mason Miller has two amazing pitches — his fastball and his slider — and they both work really well together. This led him to having one of the highest K% in the league at 44.4% in 2025.

However, when trying to be a starting pitcher, those pitches might start dominant, but it'd be hard to maintain their effectiveness. His fastball won't reach the same velocity heights as it does now, as starters need to be able to throw more pitches and stretch across multiple innings instead of only throwing all-out for one. The velocity is not going to be sustainable, which means he either needs to throw it slower, or the Padres can expect that his outings won’t be as long as the other starting pitchers, meaning more work for the bullpen.

His slider also has the potential to miss, with a BB% of 12.0, good for the bottom 6% of the league. When you only have two effective pitches, and one of them isn’t working, batters are going to know what is coming; regardless of how good that pitch is, batters will be able to adjust and jump on that pitch to cause damage. Mason Miller would need to add another pitch to his arsenal, but last season he only threw a changeup 2% of the time. It'd be a steep learning curve to get that pitch up to par with his others.

Not only that, but when you face batters multiple times in an outing, they tend to be very good at adjusting. Going through the batting order multiple times, hitters are more familiar with what is being thrown, and the averages show that they are getting on base more. For pitchers who had three to six pitches within their arsenal:

• 1 TTO: +0.07 RV/100, .316 wOBA (140K total pitches)
• 2 TTO: +0.01 RV/100, .318 wOBA (123K total pitches)
• 3 TTO: -0.35 RV/100, .335 wOBA, (70K total pitches)

With fewer pitches, those numbers are only going to go up, meaning Mason Miller will be even less effective as the game goes on as he pushes deeper into a game.

Relievers are also being used more now than they were ten years ago. In 2015, Relievers pitched 15,184 innings, while this past season they have pitched 17,863. [Those numbers might be slightly skewed as openers didn’t exist during that time, but that's still a good demonstration of how relievers are still being utilized more than they previously were.] Part of the reason the Miller trade was seen as good for the Padres was that it shortened the game. The Padres got another dominant reliever that would be able to come in and shut down a late inning, putting less pressure on the starting pitching staff. One inning of Mason Miller is worth more than, say, three innings of a No. 3 starter, which would be behind Nick Pivetta and Joe Musgrove as it currently stands. 

Miller also has an injury history that can’t be forgotten. In 2023, when he was a starter, he was diagnosed with a mild sprain of the ulnar collateral ligament in his throwing elbow, which prompted him to be shut down from throwing. He ended up on the 60-day injured list; once he returned, he transitioned to relief pitching. During his debut before that injury, he threw 15 pitches above 100 MPH across 4 ⅓ innings, which shows that he can maintain that velocity, but it will come with a cost. The best ability is availability, and having someone that can lock down an inning is always going to be valuable come October.

On the surface, moving Mason Miller to the starting rotation looks both intriguing and cheap, given the market for starting pitching right now and the Padres' finances, but it becomes far less convincing when you account for what needs to change and what the Padres would need to give up in order to get it. The Padres might be tempted by Mason Miller the starter, but Mason Miller the closer is a known commodity. The Padres need more, not less, of those right now.