Name: Joel Diaz
Weight: 210 lbs.
Acquired: IFA, January 15, 2021 (San Cristobal, Dominican Republic)
2022 Stats: 16 G (10 GS), 55.1 IP, 62 H, 37 R, 36 ER (5.86 ERA), 25 BB, 51 K, .340 BABIP (Low-A)
Signed by the Mets on January 15, 2021, the first day of the 2021-2022 international free agent signing period, right-hander Joel Diaz had a phenomenal debut season. Assigned to Dominican Summer League, the 17-year-old posted a 0.54 ERA in 50.1 innings, allowing 29 hits, walking 9, and striking out 63. Since 2010, only Sixto Sánchez has posted a lower qualified ERA in his age-17 season, posting a 0.50 ERA in 54.0 innings with the GCL Phillies in 2016.
The young hurler gained a massive amount of helium this past winter as a result, and the Mets seemed to have a second promising international free agent hurler in their ranks, with Robert Dominguez having impressed scouts and evaluators when he was signed roughly a year before. Diaz came stateside in 2022 and was assigned to the St. Lucie Mets in late May. Much like Dominguez’ results did not match the hype prior to his Tommy John surgery, the 18-year-old Diaz did not really have the best results in St. Lucie, posting a 5.86 ERA in 55.1 inning, allowing 62 hits, walking 25, and striking out 51.
Diaz throws from a three-quarters arm slot, short-arming the ball and really folding over and dropping when pushing off the mound, giving him a lower release point. He stands an even 6’ tall and weighs 210 pounds, giving him a solid frame for starting at the present with his thick trunk suggesting the possibility of further growth and/or more muscle mass in the future. The right-hander throws four pitches: a four-seam fastball, sinker, curveball, and changeup.
His fastball ranges between 92-95 MPH, averaging 94 MPH so far this season. Though the 2200 RPM it has averaged is not particularly high, the pitch has some ride up in the zone thanks to its flatter vertical approach angle, and batters have had trouble squaring up on it, as all balls put in play have averaged a 71.1 MPH exit velocity. His sinker has shown a bit more variance in its velocity, sitting 89-96 MPH and also averaging 94 MPH. The pitch has averaged slightly above-average spin rates for a sinker and has featured slightly above-average vertical and horizontal break as compared to the average MLB sinker this season.
His curveball ranges between 75-81 MPH, averaging 79 MPH. The pitch features 11-5 shape and flashes above-average possibility. His changeup sits in the mid-80s, averaging 86 MPH. The pitch features a low spin rate, giving it good fade and tumble. In the DSL, he tended to rely on his fastball and changeup until the second time through the order, but with St. Lucie, his curveball has been his primary secondary pitch, only throwing a handful of changeups per game. At times, he has struggled with his curveball command, and throwing it more frequently this season, his walk rate has risen as a result.
After getting a ton of post-sleeper helium last winter on the strength of a really great professional debut in the DSL, Diaz was only so-so in the Florida State League this season, but the numbers only tell part of the story. He was extremely young for the level, the underlying data for his pitches was good, and he has a presence on the mound. There’s work to be done, sure, but assuming he stays healthy, I could see Diaz not only shooting up Mets top prospect lists next year, but shooting up national prospect lists as well.
Diaz didn’t blow the doors off like we might’ve hoped this season, but there were some positives to take from his age-18 season. His changeup flashed plus as the season went on, always a nice development from a young arm. There were things to like about both his fastball and curveball as well, but his control of both led to middling results more often than not. That’s a fine result for a teenager getting into full season action during their first season stateside even if the ERA was ugly. He’s projecting like a back-end starter with plenty of time to gain a half-grade here or there and be something special.
Diaz followed up his otherworldly 2021 in the DSL as a 17-year-old with a difficult 2022 in St. Lucie as an 18-year-old. Still extremely young for the level, Diaz struggled to find the zone and miss bats against full season hitters, striking out fewer than nine batters per inning, and walking over 10% of the batters he faced. Still extremely young and raw, Diaz will look to build on his first taste of full-season ball in 2023, and could benefit from spending a little more time in St. Lucie before moving on to Brooklyn.