Free Agent Target: Mariners could look to strengthen bullpen with Robert Stephenson

The Mariners, historically, haven't invested heavy resources into their bullpen. Looking to contend for an AL West division title, they would be smart to break that trend and invest some capital into their bullpen.
Tampa Bay Rays v Minnesota Twins
Tampa Bay Rays v Minnesota Twins / David Berding/GettyImages

The Mariners will need to keep their options open this summer. They have a few holes to build and if we have learned anything, the free agents that they bring in, will not be high-dollar guys. I would bet almost anything that they will not be in the running for the Josh Hader, Craig Kimbrel type of relievers. The Mariners pride themselves on finding and developing overlooked guys into very solid contributors. But occasionally, you have to dip your toes into the water and acquire some legit talent. You can still work your magic, tweak some things here and there, adjust pitch usage, as we will talk about in a minute, or alter a repertoire altogether.

That arm for me is Robert Stephenson. Stevenson had two very different halves of 2023. He started out with the Pittsburgh Pirates and really struggled, in 14 innings, he had a 5.14 ERA with pretty solid strikeout numbers, but serious control issues, a 10.9 K/9 and a 5.1 BB/9.

At the beginning of June, he was traded to the Tampa Bay Rays and things completely turned around. He was one of the best relievers in all of baseball from that point on. In 42 appearances with Tampa Bay, he threw 38.1 innings with a 2.35 ERA. He put up some absolutely ridiculous strikeout numbers, 14.1 K/9, and really controlled the walks, 1.9 BB/9.

What was the reason for the breakout campaign for the 30-year-old reliever? If you look at his baseball savant page and compare 2022 to 2023, you will see exactly what changed. In 2022 he relied heavily on a slider fastball combination, throwing the slider 50.5% of the time and the fastball 47.8% of the time. In 2023, he introduced a cutter that was elite! His cutter has some of the highest spin rates in baseball at 2874, and it produced a minute .253 slugging percentage. He threw the cutter 41.4% of the time, a slider 24.1% of the time, and a fastball 23.6% of the time. This switch in repertoire and pitch usage took his average exit velocity given up from 90.6 mph in 2022 to 87.0 mph in 2023.

Even with those numbers, I think there is still some room for him to get better, which is crazy to think about. His fastball got destroyed in 2023! He threw it 23.6% of the time and that pitch had a .575 slugging percentage against it, with an average exit velocity of 93.2 mph. Those are not good numbers. I think cutting that back to around 10% or less, and increasing the usage of the cutter, which has proven to be an elite pitch, would produce even crazier numbers.

Stephenson is in his first trip to free agency, after earning $1.75 million as an ARB 3 guy, so he will most certainly command a raise. He was worth about 1 win, depending on the site you look at. He has sort of been a journeyman reliever, spending time with 6 teams since the beginning of 2020. With that and his sort of up and down and mixed results, I don't think his contract will be outrageous. He was very good in the second half of 2023, though, and I expect him to capitalize on that. I think something along the lines of maybe a 2-year deal worth $8 million, giving him $4 million AAV is a fair price to pay.