The Mariners new look bullpen

We knew Jerry Dipoto wasn’t going to sit out this trade deadline. Not with the Astros looking weaker than they have in a couple of seasons and the Athletics suddenly a couple of games behind the Mariners. The only questions were which positions he was going address and how many moves he’d make to get there. His first move seemed fairly innocuous, adding RHP Sam Tuivailala from the Cardinals on Friday. But yesterday afternoon, Dipoto swung two trades in quick succession, getting LHP Zach Duke from the Twins and RHP Adam Warren from the Yankees. With those three new additions, the Mariners have a completely new bullpen to work with down the stretch.

For quick reference, here are the three incoming pitchers alongside the three pitchers they’re likely replacing (barring any last minute surprises).

Almost across the board, the Mariners upgraded the back of their bullpen. Warren, Duke, and Tuivailala might not have much name recognition but they’re each extremely useful pieces. With these additions, the Mariners bullpen is projected by the FanGraphs depth charts to produce the third best ERA and the fifth most fWAR over the rest of the season. Let’s take a brief look at each of the pitchers added to the bullpen.

Adam Warren

With Zach Britton in New York now, the Yankees has a significant surplus in their bullpen. Adam Warren was never going to be more than a mop-up, back-end reliever in New York. That’s a role that wastes a lot of Warren’s talent. With the Mariners, he should slide into the role Chasen Bradford was holding—a middle reliever who has some flexibility to go multiple innings. I should note that he has some experience in the starting rotation too, though he hasn’t started a game since 2016.

Over the last few years, Warren has increased his strikeout rate from around 19% all the way up to 29% this year. That exponential improvement is largely due to a significant change to his pitch mix. Warren has four pitches in his repertoire: a rising four-seam fastball, a decent changeup, and two different breaking balls, a slider and a curveball. Over the last two seasons, he’s focused on throwing just his fastball and slider the vast majority of the time. But rather than his slider driving his whiff rate like we might expect, it’s been his fastball. His slider generates a whiff around 25% of the time a batter offers at the pitch, a rather pedestrian mark for a relief pitcher in this era. His fastball has a whiff rate just under 30%, which is in the 92^nd percentile among all fastballs thrown at least 100 times this season.

Despite the elite whiff rate he’s getting off his fastball, opposing batters are hitting it extremely hard when they do make contact. Per Statcast, the average exit velocity off his fastball is 91.1 mph with an almost ideal launch angle of 24 degrees. Those combine to estimate a .566 xwOBA on contact, the fifth highest mark among all fastballs thrown this season. That’s a significant red flag and could be a sign of trouble ahead. Hopefully the friendlier confines of Safeco Field will help him suppress the effects of all that hard contact.

Zach Duke

In almost every conceivable way, Zach Duke is an improvement over Marc Rzepczynski as the designated left-handed specialist in the bullpen. Since 2015, Duke has held left-handed batters to a .261 wOBA with a 4.3 strikeout-to-walk ratio. He’s allowed just a single home run to a left-handed batter in the past three seasons and has yet to allow a dinger this year.

Duke has been advertised as a left-handed specialist—and that’s a role he should excel in—but I wonder if he’d also be useful as a ground ball specialist. That’s one of the skills that’s sorely lacking in the Mariners bullpen. Edwin Díaz, Alex Colomé, and James Pazos each have a ground ball rate just above average but only Pazos has a role flexible enough to enter the game at any point to kill a rally with a double play. Duke’s bowling ball sinker helps him generate plenty of ground ball contact. But against right-handed batters, he will mix in a diving changeup that generates a ground ball 86% of the time it’s put in play! Hopefully Scott Servais won’t be extremely rigid when deploying Duke out of the bullpen like he was with Rzepczynski.

Sam Tuivailala

Of the three relievers added this week, Sam Tuivailala will be the only one who will be under team control past this season. Tui’s one of those guys whose results lag behind his raw stuff. His four-seam fastball averages 96 mph and its whiff rate sits in the 84^th percentile—not as elite as Warren’s fastball but it comes with the same hard contact red flags. Statcast estimates a .554 xwOBA on contact off his four-seam fastball, though much of that potential damage comes when facing left-handed batters. Because of his fairly significant platoon splits, Tuivailala fits as a right-handed specialist in the bullpen—the new ROOGY if you will.

The Mariners have valued pitchers who can throw a rising fastball up in the zone but I wonder if Tuivailala would be better off focusing on his sinker more often and using his four-seam when he really needs to get a swinging strike. His sinker also has an above average whiff rate while also carrying an above average ground ball rate so it’s not like it would be a dramatic drop in effectiveness. With both Warren and Duke in the fold, the Mariners won’t need a significant contribution from Tuivailala down the stretch. He doesn’t have any options remaining which limits his flexibility, but if the Mariners have specific adjustments to his repertoire they want to make, they’ve got the depth to do that now.

Yesterday, John did a great job pointing out why the Mariners starting rotation hasn’t been as taxed as their innings count might indicate. While I generally agree with him, I also think the Mariners will need to find ways to save some innings as we get closer to September and October. Lengthening the bullpen is definitely one way to get there. At this point, if the Mariners have a lead heading into the sixth or seventh, it makes it much easier to pull a starter who is at 80 or 90 pitches rather than leaning on them to get through another inning or two. It also provides some more opportunities to give Colomé and Díaz a few more days off since they’ve been called on so often this season.