After their huge seven-player swap on Sunday night, the Padres and Mariners returned to the same well and struck a smaller deal in the waning minutes before the trade deadline. Taylor Williams is headed to San Diego to join his former bullpen-mates Austin Adams and Dan Altavilla, while the Mariners receive a player to be named later — though the player has already reportedly been named: right-hander Matt Brash. The framework of the Williams deal was established during the negotiations for the bigger trade, but the trigger didn’t get pulled until just before the 4pm EST deadline.

Even though they had acquired Trevor Rosenthal, Adams, and Altavilla in the last few days, the Padres were still looking to improve their bullpen. The health of Adams’ knee is still a question mark and the inconsistent Altavilla is more of a work-in-progress than a sure-thing. In Williams, the Padres get a reliever who can contribute right away. He had been the Mariners de facto closer for much of this season and had shown some promise as a high leverage reliever. He had pushed his strikeout rate over 30% this season and lowered his FIP to 3.50. But he doesn’t come without a few warts. His command leaves a lot to be desired as he’s been prone to overthrowing in particularly stressful situations.

The biggest driver of Williams’ success this year has been an increased reliance on his wicked slider. He’s now throwing his breaking ball more than ever and it’s been extremely effective for him. Opposing batters are whiffing almost 50% of the time they offer at the pitch. What’s even more encouraging is he’s using it more often earlier in counts to steal called strikes while still burying it for whiffs with two strikes.

The results he’s getting with the pitch are excellent, and its physical characteristics are unique in baseball. He throws it around 86 mph with an average spin rate of 2466 rpm, but despite the above average velocity and spin, the pitch doesn’t really break all that much. It’s vertical movement is merely average for a slider thrown at that speed and it simply doesn’t break horizontally all that much. All the spin imparted on the pitch is nearly entirely gyro spin, or in layman’s terms, spin that doesn’t contribute to a pitch’s movement. Williams’ slider is thrown with just 7% active spin, the least spin efficient slider thrown by any pitcher in baseball.

Here’s what that looks like in practice:

That movement profile allows him to locate the pitch in the zone like he was throwing a hard 12-6 curveball. Paired with a hard fastball that gets tons of arm-side run, his two-pitch arsenal stands out among all the other fastball-slider relievers that are so popular in baseball these days.

The return for Williams is Matt Brash, a 22-year-old 2019 fourth-round pick from Niagara University. He only compiled 5.1 professional innings in 2019 before being shut down for the year, and with the minor leagues out of action in 2020, he really hasn’t had any time to establish himself as a professional. Here are Eric Longenhagen’s notes from his brief time at Low-A last year:

Brash was 93-95 in my brief look at him last year, his fastball has traits indicative of impact vertical movement and would pair nicely with a vertical breaking ball, which he has shown some proclivity for. Based on how gangly he is and how noisy his delivery is, I have him projected as a potential relief arm, likely a developmental one because of his small school pedigree and the fact that COVID and a trade will probably complicate his growth.

He’ll be an interesting project for the Mariners pitching development group. They’ve shown an ability to squeeze additional velocity out of their pitchers. He already profiles as a strong relief prospect, but with a little extra oomph on his fastball, he could have a ceiling as a high leverage reliever. Besides developing a vertical breaking ball, he also possesses a solid changeup with good tumble and fade, giving him the fuller arsenal of a starter if the Mariners want to take that development route.