Evaluating Carson Kelly as a receiver


Photo taken by Kat Allen : @kat_allen311

When Carson Kelly was called up to the St. Louis Cardinals on Sunday, it was presumed that baseball’s second-best catching prospect would assume primary duties behind the plate in the absence of Yadier Molina. After all, it’s widely believed that Kelly is good enough already that he might start on a handful of MLB teams if his playing time weren’t blocked by a future hall of famer. While the projection systems aren’t quite as high on the 23-year-old, Fangraphs Depth Charts still projects him for perfectly competent 1.2 WAR per 450 plate appearances, which ranks 33rd among all catchers.


Thus, when Francisco Pena started the first game after Carson Kelly’s call-up, a few eyebrows were raised. When Pena started the third game after Kelly’s call-up, a few more eyebrows were raised. Most fans agree that Kelly gives the Cardinals a better chance to win than Pena. It appears that manager Mike Matheny may not agree, however, based on the small-sample-time-share that’s been deployed. Additionally, Matheny’s comments from March regarding Kelly’s ability to block balls in the dirt and his “disappointment in Kelly’s pitch receiving” in Spring Training, despite his reputation as a premium defender, suggest he isn’t ready to hand over battery duties to the former Minor League gold glover.


Luckily for us, we can quantify catcher defense to various extents. For example, Baseball Prospectus rated Kelly as 3.4 runs above average defensively in limited time last year accounting for his framing, blocking, and throwing. In addition, Statcast allows us to use pitch-by-pitch data to evaluate Kelly’s pop-time and framing. I’m choosing to focus on framing because it gives us a larger sample size to work with, which might make it more likely to actually mean something about Kelly’s talent.


To quantify framing, I used Statcast data from Baseball Savant to identify all pitches which the catcher received in the area defined as the “edge” of the strike zone and which the batter did not swing at. Next, I found how many of those pitches resulted in a called strike. We’ll label the ratio of called strikes on the edges to total pitches on the edges as “Edge K%.” Here’s how Kelly stacks up since arriving in the MLB last year, compared to Molina, Pena, and the rest of the MLB since the start of last season through May 8th.

While Kelly’s Edge K% is the lowest among the three Cardinals featured, he’s still above the league average and not far off Molina’s mark. Of additional note, Kelly’s Edge K% in his lone start this year was 57.6%, which included 19 called strikes in 33 edge chances.


In hopes of getting a clearer picture of Kelly’s framing ability, I went back to Monday’s game and identified the edge pitches which he earned called strikes on, pitches that were out of the zone he gained strikes out, and pitches in the zone which were called a ball. With the help of @cardinalsgifs, we can visually analyze his performance behind the dish.


Glove side framing


Of the 19 called strikes on edge chances, 10 were on Kelly’s glove side. Below is a frame job I thought was representative of those 10 – Kelly sets up outside with the glove aligned with the center of his body before receiving the pitch with a firm hand and slight flick toward the zone. This was about perfect.



High framing


Here, Gant misses his spot badly toward the top of the zone. High strikes are the toughest to get called, but we see Kelly receive the ball similarly to the pitch shown previously. Again, well done.


Low framing miss


Now we start getting into the bad. Matt Bowman paints the low-inside corner perfectly with a sinker. This time, however, Kelly reaches down to receive the pitch before pulling the glove back up. The downward reach and pull up is much more noticeable and may have cost Bowman a called strike.


Low breaking ball framing misses


Here’s where we see the biggest issue. First, a second inning curveball from Gant. While the pitch may have crossed the plate just slightly below the knees, Kelly’s downward stab ensured the pitch was called a ball.

Next up, another curve from Gant. This time, Gant’s curveball clearly crosses inside the strike zone. But instead of freezing the glove at or near the knee, Kelly chases the ball down and pushes it outside the strike zone. It’s called a ball.

Lastly, a Matt Bowman slider. On the first pitch of the at-bat, Bowman slings his slider perfectly at the batter’s knee. Kelly, however, drastically overestimated how far the pitch would break. He dropped to block a ball that should’ve been called a strike had it been received well. Instead, Bowman found himself in a 1-0 hole.


What do the numbers say?


After seeing Carson Kelly struggle on balls low in the zone, especially breaking balls, I went back to get more granular with the data. This time, I isolated Edge K% for low-edge breaking balls (curves and sliders), low-edge non-breaking pitches, and combined the left, right, and high edges of the zone into a “non-low edge” category. Essentially, I wanted to see if Kelly’s struggles with low pitches are the result of an individual inefficacy or if all catchers struggle with these types of chances.



Thus far in his career, Kelly is above average at framing pitches on the high, left, or right edges of the zone. He drops to average when framing low non-breaking pitches, like fastballs and changeups. He is significantly below average at framing low-breaking balls. In fact, his Edge% on low breaking balls is the fourth lowest among 85 catchers with at least 30 chances since the start of 2017. It does appear that low pitches, especially low breaking balls, are harder to frame than others, but Kelly’s skill relative to the rest of the league deteriorates significantly on lower pitches.


For another reference point, Yadier Molina scores a 55.8% / 41.7% / 28.9% across the board. Kelly has been better than Molina on "non-low edges," worse on low-edge, non-breaking pitches, and significantly worse on low-edge breaking balls. Kelly’s data represents a small sample, but it aligns with what we saw in the eye test.


My first thought was that Kelly’s poor framing on low pitches might be due to his height, though upon further research I found that at 6-feet 1-inch he’s only about one inch taller than the average catcher and that catcher height has no effect on catcher framing. Maybe it’s as simple as low pitches being difficult to frame and low breaking pitches being even harder to frame. Maybe as a fairly recent catching convert, Kelly hasn’t fully adapted to low pitches yet. His ability on “non-low edge” pitches suggests potential is there for him to be a plus framer all around.


Carson Kelly is a premium defensive prospect at perhaps the most important defensive position. However, he still has more work ahead to become a premium defensive player and to earn his manager's trust.