Jairo Diaz appeared nearly fully formed when the Rockies traded Josh Rutledge to the Angels for him after the 2014 season. The 24-year-old right-handed reliever seemed to have figured something out in 2014, as he started out in High-A, then moved to Double-A midseason and received a big league call-up late in the year.
In that abbreviated stint, he threw 5⅔ innings for the AL West-champion Angels, allowing two runs while striking out eight and walking three. Across the two minor league stops, Diaz hurled 64⅔ frames of 3.48 ERA ball while putting up an impressive 11.8 K/9 rate, combined with a respectable 2.8 BB/9. That led PuRPs voters to place him at number 28 in the winter list last year.
Interestingly, all of this progress occurred after Diaz had spent several years with the Angels as a catcher after signing with the organization in 2007 out of Venezuela. After two seasons in the Dominican Summer League trying (and failing) to hack it behind the plate, Diaz moved to the other side in 2010 as a fireballing pitcher. The Venezuelan moved up and down the minor league ladder as a reliever before his big break in 2014.
When Colorado acquired him, it was expected that Diaz would be in contention for a bullpen spot in 2015. With that said, since Diaz had thrown just 32⅔ innings at the AA level in 2014 before his big league promotion, it wasn't surprising that initially he was sent to Triple-A Albuquerque to begin the season.
In 55 innings across 47 games for the Isotopes (against hitters on average that were three years older), Diaz struggled relative to his 2014 success. Specifically, though his 8.2 K/9 rate was acceptable, his 6.1 BB/9 rate certainly was not, nor was his 4.58/5.44/1.60 ERA/FIP/WHIP combo.
Nonetheless, the Rockies needed arms for the bullpen in late August and Diaz was there to answer the call. Just as he had in Los Angeles the year before, Diaz stepped his game up at the Major League level. Across 21 games, Diaz threw 19 innings of 2.37 ERA ball (3.56 FIP) while maintaining a 8.5 K/9 and reducing his BB/9 to 2.8. In those 21 appearances, Diaz allowed a run only three times, and in only one of those outings were there multiple earned runs allowed.
Diaz finished strong — his final outing of the year was a 1-2-3 eighth inning of a 3-2 game in which he struck out the side on 13 pitches in game 161 against the Giants.
From a stuff perspective, Diaz is a potential relief ace out of the pen if his command improves. From MLB.com, who placed Diaz 25th on their list of Rockies prospects recently:
Diaz arrived (from the Angels) with a plus plus fastball that rates at the top of the scale and automatically became one of the best heaters in the system. He'll sit 97-98 mph consistently and can hit triple digits. He combines it with a solid average slider that can miss bats when he's throwing it well. Diaz also has a below-average changeup that could give hitters another look, but he doesn't really need it much pitching in short relief. The biggest issue for Diaz has been his command and control ... If Diaz can get back to commanding the baseball consistently, he has the two-pitch power arsenal teams like to see coming out of the bullpen to close games at the highest level.
The way Diaz pitched down the stretch for the Rockies is obviously an exciting what-if for the big league bullpen over the next few years, but the underlying struggles with command he's had in Albuquerque mars this optimism somewhat.
Diaz just missed my ballot this time around and I suspect he won't be eligible the next time we do this list, but I hope the Major League version of Diaz has success with the Rockies in 2016 and going forward.
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