3 rentals the Mariners could Use to restock the bullpen

The Mariners' pen has been marred by injuries, but we have seen unexpectedly strong performances from Austin Voth and Trent Thornton. Voth made the club, largely due to Matt Brash getting TJ surgery, and has put up a 3.16 ERA in 24 appearances. Thornton, who throws his sweeper more than any other pitch in his mix, is in the 86th percentile in barrel rate, exit velo, and hard hit %. While these performances are encouraging, it would be unwise to rely on these arms for high-leverage situations over a full season.

We're expecting Santos back in July, but the Mariners could use a right-handed reliever with high-leverage experience. If Munoz does re-aggravate his lower back or if there is another unforeseen injury, it'd be great to have another righty in front of Stanek on the depth chart. Here are three relievers we can categorize as "rentals" since they are free agents in 2025.

Rental #1: Kenley Jansen

Kenley and his 429 career saves are reportedly as good as gone by the deadline in Boston. The 4X All-Star throws his 92 MPH cutter 90% of the time, but the lack of variance doesn't stop him from getting results. He's got a 2.89 ERA in 2024, with an impressive 33.4% K rate. His 1% chase rate indicates that guys are really swinging and missing in the zone, which is a testament to his cutter. His playoff experience as a World Series Champion, in conjunction with his 400+ saves, would be a huge addition to this Seattle bullpen. Obviously, Jerry and the Seattle org have demonstrated the ability to develop pitching, but it's difficult to artificially replace the value of a respected veteran with a resume like Jansen in the pen.

If Jerry were to call Craig Breslow about Jansen, it likely would cost close to nothing if the Mariners were willing to eat the remainder of Kenley's $16M salary. While the idea of not having to trade any prospect in the top 30 is an attractive prospect, most of us probably wouldn't name the Mariners as a typical suspect for eating salary in a trade as opposed to dealing from talent. John Stanton has expressed a willingness to spend money, so we can't rule it out.

Option #2: Paul Sewald

Imagine if the Mariners got their old closer back? Sewald hasn't been healthy for a good portion of the year but has a 2.57 in 31 regular season games for the Snakes. Paul is a prime example of the Seattle pitching lab, with a 5.50 career MLB ERA with the Mets in 125 appearances before closing 52 games for the Mariners over a three-year period. Sewald has a two-pitch mix, a 91 MPH four-seam, and a sweeper. He's a non-traditional closer without a big fastball similar to the Yankees closer, Clay Holmes. It may not be en vogue, but a closer needs to get outs. Who cares if the four-seam is 91 or 98, right?

If the Diamondbacks continue to fall down the Wild Card ladder, there's really no way Sewald stays in Arizona. Too many contenders will bid for his services, as guy with 9th inning experience who doesn't have a huge salary figure. Last year, he had a 30%+ K rate on both pitches, but that sweeper is what really makes Sewald special as a reliever. This is Paul's year to test the market, so he has a chance for a nice payday if he can show flashes of dominance down the stretch. What better place for the occasion than the park where he made himself a brand name reliever?