Entering 2019, the Pirates seemingly had a solid long-term plan at catcher. Francisco Cervelli and Elias Diaz would once again split starts, reuniting arguably the game's best catching tandem in 2018. After that, Cervelli would likely sign elsewhere as a free agent and Diaz -- who showed unprecedented offensive potential in 2018 -- would be the man.
As we near August, and the Pirates languish closer to last place in the NL Central standings and fall further away in the wild card chase, that plan looks shot. For Cervelli, it's been recurring concussions — both player and team are concerned more for his long-term quality of life than his short-term career prospects. As for Diaz, he has devolved from a rare power-hitting threat behind the plate to a guy who has had difficulty getting the ball out of the infield. What's behind Diaz's 2019 power outage? Let's take a look.
As a minor leaguer who was considered a mid-level prospect, Diaz never displayed much power. His on-base plus slugging percentage (OPS) in the minors was a modest .686 in more than 2,500 plate appearances. In more than 750 PA at the Triple-A level, Diaz had a .668 OPS. Considering his struggles as a rookie with the Pirates in 2017 -- his park-and-league-adjusted OPS was 47 percent worse than the overall MLB average (53 OPS+) -- and his relatively advanced age for a prospect, Diaz looked like a career backup.
And then, he started raking. In 277 trips to the plate in 2018, the Venezuelan backstop hit 10 home runs and posted an adjusted OPS that was 14 percent better than the MLB average (114 OPS+). Diaz boasted the sixth-highest OPS+ among all catchers who had at least 200 PA, trailing only J.T. Realmuto (130 OPS+), Wilson Ramos (130), Cervelli (123), Yasmani Grandal (120) and Omar Navarez (119).
Instead of building on that 2018 breakout, Diaz has lost his power-hitting stroke. He has just a 68 OPS+ (32 percent below the MLB average) in 2019, which places him among the five worst-hitting catchers with 200+ PA:
Diaz hasn't been very good against fastballs this season (he's slugging .342 against heat this year, per MLB Statcast), but he wasn't exactly crushing velocity last year either (.385 slugging percentage). The major difference is his performance against breaking and off-speed stuff. In 2018, Diaz crushed five home runs off curveballs and sliders and had a .530 slugging percentage. He ranked 36th in slugging percentage out of 535 MLB hitters who saw 200+ breaking pitches in 2018. He displayed some thump versus off-speed pitches, too, with two homers and a .457 slugging percentage (147th out of 619 big leaguers who saw 100+ offspeed pitches).
In 2019, though, Diaz has gone deep just once on a breaking pitch and has slugged a paltry .259 (344th out of 440 batters with 200+ pitches seen). He has yet to hit a home run against an offspeed pitch and has a .393 slugging percentage (217th among 576 hitters with 50+ pitches seen). In 2018, Diaz put breaking pitches in play at an average of 89 mph. This year, that figure is 85.3 mph. He's also making weaker contact on offspeed stuff (86.8 mph in '18; 84 mph in '19). Diaz has swung and missed a little more often against breaking stuff (35.9 percent whiff rate in 2019, 31.4 percent in 2018), and much more often versus offspeed pitches (31.3 percent in '19, 18.8 percent in '18). In brief, against breaking and offspeed pitches, Diaz is making lousy contact, and less of it.
When you combine Diaz's offensive decline with his continued defensive woes (a topic chronicled in last week's Stats column), you have one of the game's worst catchers this season. Diaz has been worth -1.0 Wins Above Replacement (WAR, which measures a player's offensive, defensive and base running value compared to a waiver-wire caliber talent). That's dead last out of 28 catchers who have 200+ PA this season. Now, the question becomes: What role does Diaz play in 2020 and beyond? Is he still capable of regaining his power swing and being the long-term starter? Or is he, at 28, a backup who had a few great months back in 2018? Considering the lack of catching depth in the Pirates' system, they'd better hope Diaz is capable of more than he has shown so far in 2019.
MORE PIRATES
• Pinch-hit heroes: Pinch hitting is, for a variety of reasons, ridiculously difficult. Batters come off the bench cold, with little more than some batting cage hacks, to face what is typically a fire-breathing reliever with a wipeout secondary pitch. That's why collectively, MLB pinch-hitters have a .726 on-base plus slugging percentage this season, with a park and league-adjusted line that's 8 percent worse than the big league average in all situations. The Pirates, by contrast, have been pinch hit maestros in 2019. With an adjusted batting line that is 49 percent above average, Pittsburgh ranks third in the majors behind only the Red Sox (93 percent above average) and the Twins (55 percent above average). Among Pirates with double-digit pinch-hitting plate appearances, Jose Osuna (190 percent above average), Melky Cabrera (69 percent above average) and Colin Moran (46 percent above average) have been the best.
• Williams hit harder: Entering the 2019 season, Trevor Williams looked like one of the most interesting test cases of the "pitcher, not a thrower" concept. Detractors pointed out that while Williams' 2018 ERA was a sparkling 3.11, his fielding-independent-pitching (FIP) stats suggested his ERA should be closer to 4.50. His proponents fired back by saying that Williams would continue to overachieve thanks to savvy pitch sequencing and the ability to induce weak contact. And indeed, he did limit hard contact last year: opponents put the ball in play at an average of 85.6 mph versus Williams in '18, about 2 mph better than the 87.5 mph big league average. In 2019, Williams' ERA has spiked to 4.96 with component stats that suggest a mid-to-upper fours ERA. And opponents are connecting with more authority this year. Batters have an average exit velocity of 87.5 mph against Williams in 2019. His hard-hit rate (balls put in play at 95+ mph) has spiked from 30.6 percent in '18 to 37.1 percent in '19 (34.4 percent MLB average). The biggest increases have come on Williams' slider (85.2 mph exit velocity in '18, 87.6 mph in '19) and changeup (80.4 mph in '18, 87.6 mph in '19).
