40 in 40: Jonatan Clase, speed demon with some pop

Earlier this week, the Mariners announced their 2023 international free agent class with nine signings from four different countries. Much of the attention went to Jeter Martinez, who signed for $600k, and to Felnin Celesten, considered the second-best prospect in this class by MLB Pipeline. Celesten signed for a team-record $4.7m, which is in line with the going rate for elite international amateurs.

But projecting 16-year-olds is often a fool’s errand. Not only are these players still going through puberty, they’re adjusting to a new country and receiving world-class instruction for the first time. Perhaps nobody on the Mariners’ 40-man roster better illustrates this unpredictability than Jonatan Clase.

Clase signed in July of 2018 as a freshly-minted 16-year-old out of the Dominican Republic. When he joined the organization, he was listed at 5’8” and 150 lbs., but within a little over a year of his signing, Kate’s excellent profile noted that he quickly grew an inch and a half and put on 20 lbs. of muscle.

Even with that growth, however, Clase’s calling card — his speed — has remained the same. In 14 rookie ball games in 2021, Clase somehow was a perfect 16/16 at stealing bases, and he added 55 steals in Modesto last year across 107 games. We’ve even seen Clase’s speed in a less-formal setting:

Speed isn’t enough to turn a prospect into an MLB-caliber player, however, and Clase wouldn’t have been added to the 40-man roster this offseason were it not for two other facets of his game:

• His patience. Speed matters a lot more when you’re on base more frequently, and a walk is that much more dangerous when there’s a threat of you stealing second. While Clase did strike out a good amount last year (133 in 499 plate appearances), he also added 65 walks to put up a respectable .267/.374/.463 slash line.
• His power. Look no further than this picture from a few years ago to see how Clase has put on some serious muscle:

After hitting just four homers in 77 combined games across the Dominican Summer League and rookie ball in 2019 & 2021, Clase found some pop in 2022, compiling 13 dingers and a .463 slugging percentage. Tanquito managed to turn some gap shots into triples, too, with 22 doubles and an impressive 11 triples. For reference, Amed Rosario led MLB with nine triples, and the Mariners’ top triples hitter was Adam Frazier (!) with four.

It was that breakout season that convinced the Mariners to use a 40-man spot to protect Clase from the Rule V draft and keep him as part of the Mariners’ organization for the foreseeable future.

Of course, given that Clase has just one full season in the minor leagues, it’s hard to imagine him making an impact for the Mariners in 2023 outside of a potential pinch-runner role down the stretch. And with Julio Rodríguez locked into center field for the next checks notes 17 years, Clase will likely need to develop as a left fielder if he wants to find a starting role with the big-league club come 2024-2025.

But that’s the beauty of baseball, isn’t it? We find prospects to dream on and we watch them develop right in front of our eyes. You might need to take a trip up to Everett or down to Little Rock to watch Clase play this year, sure. But the opportunity to watch 70-grade speed from up close — combined with the ability to say “I saw him when...” — is hard to pass up.

So let’s hope for another great MiLB season from our Tanquito, and let’s hope Clase makes a case for a 26-man spot in 2024.