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The Underrated Tale of Yandy Diaz

Photo by Jeff Marquis

When fans are conversing about the latest and greatest of baseball, the name Yandy Diaz will more than likely not come up. In fact, before reading the title, you might have never even heard of his name. This makes sense - Yandy is far from being a Top 10 hitter and has been unspectacular throughout his career. Dedicated sabermetric-focused fans may know him for his insane groundball rate. As of May 18th, Diaz has produced a 56.3% groundball rate in 2022 - 12 percentage points above the Major League average. This is not an outlier - his career groundball rate is 54.3%, serving as a vivid example of a player with a constant batted ball profile. Despite this, Yandy is one of the most consistent players in baseball.

Before I explain his undervalued attributes and his potential for success, I want to explain his journey to the show. He was signed as an international free agent by the Cleveland Indians (now Guardians) out of Cuba in 2013. Not a very highly-touted prospect, he was only signed for $300K. From there, he slowly worked himself through the Indians organization. Being promoted and demoted several times up and down the minor league system, he made his debut with Cleveland in 2017. Playing in 49 games that season, he managed a .306 wOBA (.328 expected) with an 84 wRC+ and 0.2 fWAR. His fielding was nothing to care deeply about, and he was demoted the following season. In late 2018, he became an official Major Leaguer, never being sent down again. Through 39 games, he carried a .346 wOBA, but still only earned 0.2 fWAR. The Indians did not see much value, so they sent him off to Tampa Bay in a three-way deal that returned them Jake Bauers. Perhaps they disliked Diaz’s average launch angle and groundball rate - both generally serve as indicators of sustainable future success. Yet in that same line of thinking, they clearly ignored the hard-hit rate, a metric that justified his performance at the time. The Rays overlooked his lack of flyball production, correctly identified his value, and gave him the sample size to prove his worth.

Adjusting his hitting approach a bit, Diaz produced career-highs in OPS, fWAR, wRC+, and ISO in 2019 through 79 games. He was not an everyday player, but Chaim Bloom’s (Senior VP of Baseball Ops for Rays) hunch was becoming true. Unfortunately for Diaz (and the rest of the world), the COVID-19 Pandemic hit next season, taking up an important part of his career. Yandy produced good numbers through his 34 games played, but I am hesitant to use 2020 data as evidence of success. 2021 offered more opportunities. Diaz regressed from his 2019 highs (most notably, his wOBA dropped 16 points), but he played his first full Major League season, logging 134 games.

On top of that, another trend was becoming apparent - Yandy had a keen eye at the plate. And while I am not one to be an anti-strikeout absolutist, I can appreciate a hitter’s ability to go down with consistent contact. By definition, the BABIP of a strikeout is .000. The BABIP of any ball in play is exponentially higher, giving the hitter a better chance to reach base. Certain run expectancy matrix probabilities will devalue the difference between a strikeout and batted ball event (BBE) in the aggregate. But with no runners on or no force double-play opportunity, I’d much prefer contact. It is worth mentioning that the level of contact can completely cancel out the former concept. Flyballs routinely have a higher wOBA than groundballs, being worth about 50% more by some estimates. Given this, a high-strikeout hitter with a great flyball rate could outperform a low-strikeout hitter with a mediocre flyball rate. Yandy may be at a natural disadvantage by trailing his opponents in hitting the ball upwards, but his skill at making contact has more than compensated for that.

As the 2022 season trudges on, Yandy Diaz’s trademark low-launch angle approach has earned him a spot as one of MLB’s top 100 hitters. Using xwOBA (expected wOBA, the premier hitting metric used to measure players), he ranks 73rd with a .360 clip. Standing one spot below Anthony Rendon, he is in good company. The average sabermetrician would expect that he finally fixed his groundball issue, and his stats are adjusting accordingly. As mentioned earlier, this could not be farther from the truth. In that case, his Barrel % (balls hit within the ideal launch angle and exit velocity range) must be improving. No, he is producing about 45% fewer barrels than his average. With these two factors ruled out, what is the reasoning behind his jolting success this season?

Based on the conglomerate of Baseball Savant data, his success can likely be owed to his improved plate discipline. His first-pitch strike percentage is down 5.4 points. His whiff percentage is down 5.1 points. First-pitch swing percentage, chase percentage, and zone contact percentage (among others) have all improved. He is being more selective with his pitches, making clean contact. Pictured below is his strikeout percentage per zone, which illustrates his stellar discipline this season.

Yandy Diaz's K% by zone, according to Baseball Savant

As is evident in the graphic, the majority of Diaz’s strikeouts are happening within the zone - he is not consistently chasing pitches and failing. His 16.5% walk rate is a good side effect of the betterment in plate discipline. These surprising positive changes may only be due to a small sample size, but I believe they are sustainable. A refined plate approach can be more easily controlled than a groundball or hard-hit rate. While a player can control their actions of swinging or not swinging, they cannot control what happens to a ball exactly after it comes off the bat. A swing pattern can be adjusted to improve aggregate results, but an individual event is up in the air. Hence, I also believe that Yandy’s groundball, hard hit, and barrel rates will regress closer to the mean. This would allow for an even better season, making him produce at a rate that is above expectations.

As Yandy Diaz remained a borderline Major League player, the Rays unique knack for identifying undervalued talent allowed him to reveal his talent. His ability to make contact in a hit-or-miss league is almost unrivaled. His incredible eye has led him to be ranked in the 100th percentile for chase rate. Even though he may hit a few more groundballs than recommended, his other great contributions simply overshadow this. Assuming his batter’s eye stays constant and his hitting regresses as intended, he will continue to produce value at an above-par pace. Although this is great, he could be better. If he can address the groundball issue and alter his swing path successfully, I genuinely believe he could be one of the most lethal hitters in baseball. If you weren’t paying attention to Yandy Diaz beforehand, I hope you are now - his incredible ability to produce consistently is worth watching.

*Data as of May 19th*



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