Carson Kelly: Patience Personified

Carson Kelly has emerged as the breakout catching star of 2021.

At one point, Carson Kelly was one of the most coveted catching prospects in baseball. He was thought to have tremendous offensive upside while being a reliable defender. Unfortunately, he struggled while in St. Louis and was likely never going to get the opportunity to play as long as Yadier Molina was there. So, the Cardinals packaged him in as part of the Paul Goldschmidt deal that sent Kelly, Luke Weaver, and minor leaguer Andy Young.

Lo and behold, Kelly discovered himself in Arizona in 2019. A 107 wRC+ with 18 home runs in 365 PAs was good for a 1.8 fWAR in his first season in the desert. He followed it up with a difficult and frustrating 2020 campaign, but Kelly never wavered. Instead, he has now found the very best version of himself and has quietly played his way into being one of the best catchers in baseball this season. 

All stats are reflective of the morning of Thursday, May 13th, and will not include any games played on May 13th


An OBP Machine


Kelly was never known to have elite plate discipline. But, in 2017, Kelly started lowering his strikeout rate and raising his walk rate as he went up through the minors. Then, in his first full major league season in 2019, he had a 13.2% walk rate and 21.6% strikeout rate. That was the highest strikeout rate of his professional career, but there were some encouraging signs for his plate discipline being sustainable. 

Kelly didn’t swing a lot and was able to limit whiffs as well. In 2019, Kelly swung just under 42% of the time, which is about 5% below the MLB average. He’s selective, having an O-Swing% of about 25%, or 5% better than average. He matched that with an above-average O-Contact%, meaning it was difficult to get him to chase out of the zone for a swing and miss. That’s a great sign for sustainable success. And, moving forward, the Diamondbacks counted on Kelly to make some progress going into 2020. It didn’t exactly work out like that, unfortunately.

2020 proved to be a difficult year for the promising catching prospect. Kelly posted an abysmal .221/.264/.385 line, with a 4.7% walk rate and 22.5% strikeout rate. He was swinging more and whiffing more. He chased out of the zone and was still making contact outside of the zone, but his zone contact rate had fallen a lot. His xwOBA on pitches in the zone fell dramatically. His swinging-strike rate went up by about 2 points as well.

Compared to some guys, this won’t seem like a big deal. His strikeout rate was below average, and it was a fluky year for a lot of people. But, Kelly relied on his ability to get on base and not strike out as a way to be successful at the plate. So, fantasy managers had a tough task when it came to evaluating Carson Kelly’s plate discipline. Was 2019 for real? Was 2020 the real Kelly? What was in store for 2021?

Well, here are his ranks early in the 2021 season:

Carson Kelly 2021 Plate Disciple Statistics (min 100 PAs)

That’s right, Carson Kelly has the highest OBP in the league. Higher than Mike Trout, who is off to an incredible start this year and the best player in the league. If you’re in talks with Mike Trout in anything at any point in time, you’re probably doing something right. Kelly is one of 10 players with a BB/K ratio over 1 and is fourth in the league in that category. 

This year, Kelly is swinging at 37.6% of pitches, well below the league average. And, given his below-average zone swing percentage, Kelly may get challenged with more pitches inside the strike zone as the year goes on. This season, Kelly has an average zone contact rating but is hitting a career-high .433 xwOBA on pitches inside the strike zone. If he sees more pitches in the zone, Kelly should be ready for them. 


Perfectly Placed


Diving into Kelly’s batted ball profile, the surface-level statistics may indicate some regression is in order. Kelly ranks below average in exit velocity, max exit velocity, and hard-hit rate. That does give me some pause when first looking into it, but he’s only overperforming his xwOBA by about .04. How? To break this down, let’s get into some of his batted ball data.

Carson Kelly 2020 to 2021 Quality of Contact Metrics

The first thing that jumps out is Kelly getting the ball in the air a lot more. His average launch angle is the highest it’s ever been, so it’s clear he plans to limit the number of ground balls off the bat. Ground balls for Kelly are automatic outs since he isn’t going to be beating any balls out on the infield.

Against fastballs, Kelly held a 31.7 degrees SdLA but it fell to 21.2 degrees. You can read Alex Chamberlain’s piece about launch angle tightness and how it’s important here. (Shout-out to Twitter user @GoCubs49 for the help with the Kelly launch angle numbers) Still, if Kelly isn’t hitting the ball hard, then is hitting the ball in the air a lot more going to give Kelly the success that he’s seen so far this year? 

Kelly has a .339 BABIP early in the season, which would be the highest value in his career. That does seem to hint at regression, which means he’s not going to keep up a 191 wRC+ this year. However, his xBABIP is .348, which is a direct result of putting more balls in the air this year. Even if Kelly isn’t hitting the ball as hard, getting it up in the air will more likely result in hits. To put it straightforwardly, Carson Kelly is perfectly placing the ball in the field. 




Kelly is hitting .333/.481/.615 with 6 home runs, 19 RBI, incredible production from a catcher. Among catchers with at least 100 PAs, Kelly is top 3 in HRs, batting average, wRC+, and fWAR. He’s been the big breakout this year at the position and, if his early improvements in plate discipline and launch angle continue, he could become one of the top hitting catchers in the league. But, we still need to talk about the other half of a catcher’s job.


Inconclusive Defense


I can’t write about a catcher and not talk about their defense. It is the most demanding position defensively and if you have a strong defensive catcher, then you can live with the player being a below-average hitter. For example, Austin Hedges will always have a job in baseball because he is a great defender. I’ve written about how the conversation around catcher defense is misguided and the focus of it should be on framing. So, to evaluate Kelly’s defense, I’ll start with his framing. 

There are different framing statistics and they are calculated differently. We’ll start with Baseball Prospectus’s stats, where his overall CDA is 1.0, good for 10th in the league out of 83 catchers. His FrmR, framing runs, is .9, which is tied with Hedges for 10th in the league as well. Showing some above-average potential defensively, and his .8 WARP, 2nd among all catchers, reflects that potential. Kelly works with the Arizona pitching staff, which should be easier, as they have the 8th highest zone rating as a staff. 

Moving to Baseball Savant, we can see some of Kelly’s framing stats by plate zone. Kelly struggles with framing the low pitch and I believe the reason for that is Kelly is very narrow while set up on two knees. The other issue is Kelly not getting his glove low enough to work up towards the zone on low pitches, which makes it easier to snap up and frame for the umpire. While most catchers have adopted the one knee stance, Kelly remains traditional in his stance but he’s too narrow. 

Kyle Higashioka is someone that Kelly can model himself after in order to be more successful in his framing. Let’s take a look at the different stances for Kelly and Higashioka. 





Higashioka sets himself up as a wide base and keeps his glove low on the pitches he wants low in the zone so he can snap the glove back up. That enables him to earn more strikes, as he did for Gerrit Cole above.

The one knee stance that Kelly and Higashioka forego is supposed to help the catcher frame the low pitch and maintain their durability throughout the course of a season. Some have argued that the stance comes at a cost for blocking, but as JJ Cooper of Baseball America found, the difference in stance did not appear to be statistically significant. Besides, being able to frame the low pitch well is much more important to catcher defense than blocking balls in the dirt, as framing can save some strikes (and even runs) over the course of a game.

Kelly has graded out well by CDA and did have 5 runs saved on his framing in 2019, so the defensive potential is there. He doesn’t have to adopt these changes, but if Kelly wants to be able to frame the low pitch more, he could adopt the popular one knee stance or model himself after Higashioka with the wide base and low glove setup. Kelly should absolutely be making these changes to reach the next level as a defender.




Carson Kelly is taking his plate discipline to a new level. His ability to lay off pitches out of the zone and excel at hitting pitches in the zone has fueled his breakout. Hitting the ball in the air consistently, creating more flyballs and fewer groundballs (generally thought to be easy outs) will only help him as he moves deeper into the season. If Kelly can become one of the better defensive catchers in baseball, while maintaining his offensive breakout, then he could have a fighting chance at becoming the best catcher in baseball. 


Photo by George Walker/Icon Sportswire | Adapted by Doug Carlin (@Bdougals on Twitter)

Max Greenfield

Former Intern for the Washington Nationals, now a Going Deep Writer analyzing the next possible breakout pitcher.

2 responses to “Carson Kelly: Patience Personified”

  1. Logan says:

    Who You got ROS, Kelly or Contreras

    • Max Greenfield says:

      Kelly. Better plate discipline, better ability to get the ball in the air consistently.

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