While we wait to see where Giancarlo Stanton and Shohei Ohtani end up this offseason, we have been treated to almost no hot stove activity. As such, one of the more notable moves to come down the pike was a small deal the Toronto Blue Jays struck with the St. Louis Cardinals to acquire the services of Aledmys Diaz for a single prospect, outfielder J.B. Woodman. Woodman is a fringy guy not likely to be featured on many top-100 lists this winter, so chalk this one up to a tiny move most clubs make to help massage their 40-man rosters.
The only trouble with that is that Diaz is involved. It was only a year ago that Diaz garnered a healthy amount of National League Rookie of the Year votes after coming out of nowhere en route to a three-win season. The Cardinals have generated countless high-floor, low-ceiling prospects that kick around for several years in the minor leagues before putting together outstanding major league records, and Diaz appeared to be the next guy on the list. He posted a 133 wRC+ in 460 plate appearances for the Cardinals in 2016, all while playing shortstop. There’s absolutely no way a player like this could be shipped for a fringe minor league outfielder as a way of balancing the 40-man.
As goes the success of the Cardinals devil magic, so goes its failure. Diaz came crashing back to earth in 2017, like so many of his Cardinals brethren. His quality of contact disappeared, and his power followed as a result. Diaz was always playing above his head two years ago; he carried a roughly average xwOBA, while his raw wOBA soared 54 points higher. His average on balls in play was a shade high, too.
Despite some expected regression, Diaz completely fell apart at the plate last year. His xwOBA cratered to .263. His chase spiked nearly 12 points to a garish 38 percent. His whiff rate jumped more than three points. He swung at everything while his contact rate dropped by more than four points. His average exit velocity dropped by more than four miles per hour. There were no reports of injury. When all was said and done, Diaz spent three months in triple-A trying to get right. He finished his major league season with a mere 78 wRC+ in only 301 plate appearances.
Furthermore, Diaz was a power-hitting shortstop who couldn’t actually play shortstop. Carlos Correa and Corey Seager were believed to be destined for a move to third base at some point in their careers. Instead, they have both been defensively excellent in the hole. One can’t say the same for Diaz. He has been a net negative at short by all three advanced defensive metrics, and not by a small margin. One might argue that the sample size is too small for those numbers to meaningful yet, but even the eye test has corroborated his inability to perform at the most second-most important defensive position on the field.
It didn’t help that the Cardinals’ latest member off the assembly line, Paul DeJong, had a terrific season last year, slotting in comfortably at short once Diaz was benched and then demoted. Diaz looked washed up, on the verge of his age-27 season, and with a younger, shinier model ready to replace him.
Why might the Blue Jays want a player like Diaz? Well, he helps round out their 40-man roster, for one. Steamer projects Diaz to be a league average bat in a primarily backup role to the left side of the infield, whether that’s Troy Tulowitzki at short or whoever might be at third base when spring training starts. He doesn’t have the bat nor the glove to hold down an everyday job. Given his age and recent performance, he can still be a valuable 10th man, but little more.
Perhaps Diaz was hiding a nagging injury that cost him bat speed and exit velocity. Perhaps his true talent does live somewhere between his 2016 and 2017 performance. If that were true, he should still be good enough to help the Blue Jays in the short term.
I also can’t help but wonder if the Cardinals devil magic is now collecting its debt.