2018 Pittsburgh Pirates Rewind: Catchers

(Photo by Jon Durr/Getty Images)
(Photo by Jon Durr/Getty Images) /

With the 2018 season being done and the 2019 offseason not really being able to start until after the World Series, it’s time to look back at the different positional groups in 2018.  First up are the catchers.

The Pittsburgh Pirates catchers this season hit 22 home runs this past season, with Francisco Cervelli providing 12 and Elias Diaz 10.  Cervelli eclipsed his previous career high of seven on May 31.  Unfortunately for him, he was limited to just 104 games and 404 plate appearances.  That’s long been Cervelli’s problem, only posting one season with more than 500 plate appearances (2015) and just two with over 400.

While the Pirates have struggled to replace him offensively in the past – Chris Stewart, despite being a plus pitch framer, hit .197/.276/.249 in 257 plate appearances in 2016 and 2017.  This year, however, Elias Diaz provided lots of value behind the plate, hitting .286/.339/.452 in 277 plate appearances.

The emergence of the Diaz as a backup and Cervelli’s power led the Pirates to finish third in WARP, Baseball Prospectus’ version of WAR that includes framing, blocking, and throwing:


Cervelli (3.07 WARP) finished fifth and Diaz (2.25 WARP) finished 10th.  Most of that value came via the bat, as their defense lagged behind.  The club finished 22nd with -7.6 framing runs, 26th with -2.6 blocking runs, and second with 0.7 throwing runs.  Add that together, and the Pirates catcher had -3.8 fielding runs above average after adding in the those throwing, blocking, and framing numbers.  That kept the Pirates in the bottom half, ranking 19th.  There is a way to improve these defensive numbers for next season that I’ll be writing about soon, but it’s a radical and aggressive move that really wouldn’t fit the history.

Where the defense struggled, the offensive bloomed.  Cervelli adjusted his stance and saw his power play more.  Part of that came from Cervelli increasing his launch angle and driving the ball in the air more.

Over the last four seasons in which Trackman has kept track of batted ball data, Cervelli’s average launch angle’s have been of the following:

YearAverage Launch Angle
Grand Total8.3°

The distribution of his launch angle’s since 2015 looks like:

In 2018, Cervelli made contact with the ball at a higher angle and was able to hit more fly balls.  Just look at the distribution, in 2015 Cervelli was making contact with angles that would lead to more extra base hits but he was also hitting the ball at a suboptimal angle too.  The same applies to 2016 and 2017 as well.  In 2018, however, Cervelli’s launch angle distribution doesn’t have those peaks to the left of zero and the center of the distribution moved to the right.

The changing of the swing to get more loft (attack angle) helped Cervelli’s batted ball profile (launch angle) as his groundball rate decreased from 52.3 percent to 38.8 percent while his flyball rate increased from 27.1 percent to 41.7 percent.  Add in his ability to draw walks (12.5 percent) and get on-base (.378), Cervelli was a bat you’d want at the dish showing some power (.172 ISO) and on-base skill.

But again, he only played in 104 games because of injuries, so it wasn’t all rosy for catcher who will be entering his age 33 season next year.  Recurring concussion symptoms were a problem and for Francisco Cervelli going forward, moving off the position could best for him, and that’s something that John Jaso did because of the concussions.

The internal replacement would be Elias Diaz, who posted a .340 wOBA and was worth 2.3 wins.  He did this all in 82 games.  The breakout offensively helped mask the defense where Diaz was worth -1.2 framing runs and overall was -3.2 runs worse than an average catcher.  So on the surface, Diaz would be a natural replacement at catcher for the club with Cervelli moving off to a new position if the bat plays.

But what if Diaz isn’t that player going forward?  I’ve long been a skeptic of Diaz’s bat, though this season provided a glimpse of what he might potentially be able to do.  If he remains a .340 wOBA player, Diaz will be able to start at the Major League level despite his framing and blocking numbers.

When Nate Werner at Pirates Breakdown looked at the Pirates and solving their home run, he found in his model that Diaz over performed by three home runs (at the time Diaz had hit eight).  He wrote that,

"“Diaz’s difference between his HRs and PEHRs of 3.0 suggests his power is more akin to Cervelli’s pre-2018 results, rather than on par with the starter’s current levels. While a much more in-depth look at Diaz’s overall approach should be taken, we’ll leave it at this: his home run power is likely over-stated this season.”"

Nate’s model looked at balls in play and the probability each ball would be a home run in that park, which acts as a park adjustment.  The model doesn’t include spray angle, an important factor in determining direction.  A pulled down the line ball is more has a better chance of getting out compared to hitting it dead center, or in the Pirates case the notch.  Down the line doesn’t need as much power.  Here’s a look at Diaz’s spray chart using the BaseballR package from Bill Petti:

It’s a neutral field so all balls along the outer line aren’t home runs, some are outs and some are other extra base hits.  In terms of balls to the outfield, Diaz looks about even in terms of where the balls are distributed, but balls in the infield are mostly pulled on the ground to the shortstop and third baseman.

Because Diaz should have hit less home runs based on Nate’s model, using the spray chart and the batted ball data the spray angle can be calculated using the method Jim Albert laid out here.  The following are the spray angle’s of Diaz’s home runs (only nine registered with Trackman), with -45° being down the left field line and 45° being down the right field line:

HR NumberSpray Angle

Given that PNC Park jettisons out deep in left field, with only the left field corner playing favorable, you have to wonder about the power going forward with really only four of his nine tracked home runs landing before it gets deep at PNC, as around the -25° mark the fence starts to jet out.  Furthermore, Diaz only had 30 present/40 future game power and 45 present/45 future raw power when he was last a prospect.  He’s never really been projected as a batter with pop, but he does have the size to where maybe it’s not unreasonable for him to outperform his scouting grades.

Next. 2018 Pirates Rookie of the Year: Richard Rodriguez. dark

Overall, the Pirates catchers were a strong position group in 2018.  They were third in terms of value (WARP) and both Cervelli and Diaz showed power.  Despite their strong showing, there’s still questions going forward with the defense, Cervelli’s health, and if Diaz can be an everyday starter and if the bat is real.  As good as they were in 2018, heading into 2019 there should be some concern unless Cervelli is able to stay healthy or an aggressive move this offseason happens.

*Numbers from Fangraphs, Baseball Savant, Baseball Prospectus