An underrated lefty in the bullpen, Speier had the third most innings pitched out of any relievers on the team in 2023. He was also one of just two lefties on the team after Marco Gonzales ended his season prematurely due to injury. Over 54 ⅔ innings, he posted a 3.79 ERA and a 1.061 WHIP, solid numbers but they could've been even better.
He put up excellent percentile numbers, placing in the top 11% of the league in chase, strikeout, walk, and ground ball rates. In fact, his chase rate of 39.7% was the highest in the league among qualified pitchers. He was held back by below-average barrel and hard-hit rates but there are some signs that he could see a bump in performance in 2024.
First, he had an xERA of 3.50, slightly better than his actual ERA. Second of all, he had a FIP of 3.35. These two figures try to serve as more accurate measurements of a pitcher's performance, with FIP more specifically gauging a player's ability to limit the three true outcomes and xERA also factors in quality of contact for all batted balls.
While his barrel and hard-hit rates were rough, his average exit velocity was just 88.5 mph, which leads me to believe that in any given at-bat, he either gave up extremely hard contact or extremely soft contact. Out of 47 total hits, seven were doubles and seven were home runs. His sinker in particular had a high slugging percentage against of .439. A slight change in pitch usage may do him well as despite being just his third-most used pitch in 2023, his four-seam fastball had an excellent batting average against of .128 and a run value of six.
The Mariners have lost several key arms this offseason, namely Justin Topa and Prelander Berroa, but with the addition of Gregory Santos and potential improved year from Speier, Seattle's bullpen will continue to be one of the best in baseball.