The Mariners land a crucial late-inning arm

Adding a power arm to the bullpen before Opening Day was paramount for the Mariners.

Charlie Riedel / AP Images

Not long ago, Mariners GM Justin Hollander told the Seattle Sports Radio Hot Stove podcast that his team wanted to add someone to partner with the current rotation of backend relief arms. Today, Hollander acted on his words.

“If we could add something to the bullpen to continue to take the pressure off (Matt) Brash and ‘Muni’ (Andrés Muñoz) and (Justin) Topa and (Gabe) Speier at the very back end of the game, that would be appealing to us.” - Justin Hollander

The reliever Seattle landed was Gregory Santos, who the team acquired via a trade with the White Sox. In return, the Mariners sent minor leaguers Prelander Berroa and Zach DeLoach to the Windy City, along with the 69th overall pick in this year’s amateur draft.

From my perspective, there are many things to like about Santos, although there are blemishes that merit discussion too. Let’s walk through all of it beginning with the good stuff.

Youth is served

Although he made his MLB debut with the Giants in 2021, Santos maintained his rookie status through last year. Furthermore, the 24-year-old’s arrival injects a little more youth into Seattle’s talented pitching stable.

Following today’s trade, Bryan Woo and Carlos Vargas are the only pitchers on the Mariners’ 40-man roster younger than Santos - but only by months and days. All three are entering their age-24 season. The lone position player younger than the trio is, you guessed it, Julio Rodríguez.

Late-inning solution

Last year, 51 of the 66.1 innings Santos pitched were the final three frames of games. This is a particularly important aspect of the deal considering Seattle has traded away key relievers Justin Topa (mentioned by Hollander in his comments) and Isaiah Campbell this offseason, plus Paul Sewald last July.

Bringin’ the heat!

Santos’ sinker was one the hardest thrown in 2023. Only two hurlers using the pitch at least 200 times had a higher average velocity than Seattle’s newest reliever.

Highest Sinker Average Velocity (200 sinker min)

Jordan Hicks - 100.1 mph
Abner Uribe - 99.4 mph
Gregory Santos - 98.9 mph
José Alvarado - 98.7 mph
Bobby Miller - 98.7 mph
Brusdar Graterol - 98.6 mph
Gregory Soto - 98.1 mph
Lucas Erceg - 98 mph
Camilo Doval - 98 mph
Colin Holderman - 97.9 mph

MLB average sinker velocity in 2023 = 93.3 mph

For anyone wondering, the highest average sinker velo by a Mariner in 2023 was Andrés Muñoz (98.4 mph). The right-hander doesn’t appear on the preceding leaderboard since he threw just 159 sinkers last year - well under the set minimum of 200.

Devastating slider

Santos’ best weapon was his slider. Among 66 pitchers throwing the pitch at least 500 times, the right-hander’s opponent wOBA was second-lowest. The leader happens to be a new teammate.

Lowest wOBA vs Slider (500 slider min)

Matt Brash - .198
Gregory Santos - .202
Gerrit Cole - .206
Ian Hamilton - .208
Kyle Bradish - .210
Tanner Scott - .212
Spencer Strider - .216
Dauri Moreta - .221
Jon Gray - .228
Alexis Díaz - .233

MLB average vs slider = .288

Weighted On-Base Average (wOBA) is a sabermetric version of on-base percentage (OBP) that credits hitters for how he reached rather than treating all on-base events as equals, as OBP does. For instance, a double is more valuable to run production than a single, a home run more than a double, etc.

Prevented the most damaging contact

Santos held opposing hitters to an excellent 34.8-percent hard-hit rate in 2023, which was noticeably better than the MLB average (39.2-percent). But his knack for avoiding barrels was far more impressive.

Last season, 199 pitchers allowed at least 200 batted balls. None had a lower barrel rate than Santos (1.5-percent). The MLB average was 8.1-percent.

For the uninitiated, a “barrel” is a batted ball with an ideal blend of launch angle and exit velocity that leads to the most devastating offensive outcomes. Last year, 85.7-percent of all home runs were barrels. Moreover, these well-struck balls produced a .742 AVG and 2.493 SLG league-wide.

To this point, just two of 289 plate confrontations (0.7-percent) against Santos resulted in a homer last year. Among 375 pitchers facing at least 200 hitters in 2023, only Oakland’s Lucas Erceg (0.4-percent) had a lower home run rate than the native of San Cristobal, Dominican Republic did.

Keepin’ a low profile

Remember those 199 pitchers allowing 200-plus batted balls? Only four had a lower fly ball rate than Santos did. Even better, opposing hitters produced a meager .125 AVG on fly balls against him. The lowest of any hurler within our group of 199.

Santos also did a wonderful job of keeping batted balls on the ground. His 52.2-percent ground ball rate was 18th-best, although opponents did hit a league-average .248 against him.

Perhaps Chicago’s -10 outs above average (OAA) from its infield and the team’s below-average ground ball out rate led to Santos’ surprisingly average-ish success.

Maintained his control

Santos’ 22.8-percent strikeout was essentially league-average. But he was adept at limiting free passes. Compared to 162 qualified relievers, his 5.9-percent walk rate tied for 21st-best and was nearly three-percent better than the MLB average.

My Go-To Stat Likes Him Too

Thanks to Santos’ ability to limit quality contact and walks, his .276 xwOBA was top-35 among 167 MLB relievers facing 200-plus batters. As most long-time subscribers know, xwOBA is my favorite metric to use when making a snapshot assessment of pitchers.

Expected Weighted On-Base Average (xwOBA) uses quality of contact (exit velocity and launch angle) to determine what should’ve happened to batted balls. A key advantage to xwOBA is defense (good or bad) doesn’t influence it. This gives us a truer sense of how a hitter or pitcher is performing.

In Santos’ case, his xwOBA compares extremely well to key contributors from Seattle’s pitching staff.

Mariners RP xwOBA Leaders (2023)

Paul Sewald - .216 (with Seattle)
Andrés Muñoz - .268
Justin Topa - .268
Trent Thornton - .274
Gregory Santos - .276
Matt Brash - .280
Bryan Woo - .289
Gabe Speier - .290
Logan Gilbert - .297
Luis Castillo - .302
George Kirby - .305
Isaiah Campbell - .307
Tayler Saucedo - .314
Bryce Miller - .334

MLB average xwOBA = .320

He could be here a while

Santos won’t be a free agent until after the 2028 season, which means he’ll remain under club control until he’s 28-years-old. An outstanding development assuming he remains healthy and effective.

Yeah, but…

There always seems to be a “yeah, but…” with trades. This time, the pressing issue appears to be Santos’ health. The Dominican spent the final weeks of the 2023 campaign on the IL due to elbow inflammation.

Adding to the intrigue, beat writer Scott Merkin posted the following information relayed by White Sox GM Chris Getz in early December.

To this pitching non-expert, Getz’s club did seem to aggressively ramp up Santos’ workload in 2023. This becomes evident once we review his annual inning tallies across all professional leagues.

Gregory Santos’ Workload as a Professional

2016 - 41 innings
2017 - 48 innings
2018 - 49 innings
2019 - 34.2 innings
2020 - Did not pitch (pandemic)
2021 - 30.2 innings
2022 - 38.2 innings
2023 - 66.1 innings

It’s worth noting the preceding list didn’t include 11 innings Santos tossed during Dominican Winter League action between the 2022 and 2023 campaigns. Even without this workload included, the youngster threw nearly as many innings last year as he did in 2021 and 2022 combined. This seems like an alarming increase to this unqualified blogger.

Getz’s comments in December suggest it’s possible Santos’ Cactus League debut with his new club may not occur until several weeks after pitchers and catchers report, which should be fine. After all, Opening Day isn’t until March 24.

There is a non-health issue also worth mentioning. The results Santos garnered from his sinker. Even though its velocity was elite, opponents boasted an eye-popping .343 AVG and .481 SLG versus the pitch. Last season, MLB hit .284 and slugged .427 against sinkers.

Is this a reason for concern? Not at this time. To me, the difficulties Santos encountered with his sinker in 2023 represents an inefficiency a young player can work to improve upon with his new organization.

Finally

Is it risky to acquire a pitcher who just logged a career-high inning total in a season ending with an IL stint due to an elbow issue?

Sure, he could go down with an arm-related issue in Spring Training or during the upcoming season. Then again, the same can be said about any pitcher.

Personally, I’m inclined to give Hollander and President of Baseball Operations Jerry Dipoto the benefit of the doubt regarding the health of their newest reliever. They must have felt comfortable with the situation to move forward with this trade.

As for the draft pick the Mariners surrendered in the deal, I suspect it was a difficult choice by management to part with it to get Santos. For fans looking for a reason to not fret over the pick, I have an interesting, yet useless nugget for you.

For whatever reason, probably randomness, few 69th draft picks have reached the majors during this century.

Big-Leaguers Drafted with 69th Overall Pick Since 2001

Neal Cotts (2001) - 5.2bWAR
Josh Fields (2007) - 1.8 bWAR
James Darnell (2008) - -6 bWAR
Adrian Houser (2011) - 3.4 bWAR
Wyatt Mathisen (2012) - 0.0 bWAR
Marcus Wilson (2014) - 0.0 bWAR
Blake Perkins (2015) - 1.2 bWAR

Naturally, the results of previous drafts aren’t predictive when considering future drafts. But I thought this exercise might prove useful for the segment of Mariners fans who tend to dwell on the past.

To me, this trade was a no-brainer. The Mariners needed another complimentary arm to team with Brash, Munoz, and Gabe Speier. Especially after dealing Sewald, Topa, and Campbell over the last six months.

Gregory Santos checks this block in a big way.

My Oh My…