D-backs Catcher Kenny Castillo Embraces ABS System and Modern Stance Trends
Diamondbacks catching prospect Kenny Castillo discusses his Arizona Fall League experience, the ABS Challenge System, and the widespread adoption of the one-knee-down stance.
MESA — Diamondbacks catcher Kenny Castillo is in the Arizona Fall League after missing time to injuries for the first time in his career.
In terms of playing time, he’s taken a backseat to the Red Sox’s Johanfran Garcia and the Angels’ Juan Flores. He still gets 1-2 starts behind the plate each week to stay fresh, most of them coming on Thursdays.
“Sometimes you play two, three times a week, so you need to be ready all the time,” said Castillo.
In Arizona, he’s slashing .259/.344/.370 with eight strikeouts and two walks in 32 plate appearances. He got off to a hot start in the first week, but has cooled off with fewer game reps.
Opinions of the ABS Challenge System
The biggest rule change coming to Major League Baseball in 2026 is the introduction of the Automated Ball/Strike Challenge System (ABS).
It’s been in the Arizona Fall League since at least the 2019 season and was recently tested last spring.
“Yeah, I love to see that. Sometimes the umpire is not perfect; he’s human.”
The process works as follows: each team receives three challenges. The hitter, pitcher, or catcher can challenge a called strike or ball. If the challenging team fails to overturn a call, they lose it.
This year, we’ve seen some really close calls in Arizona. I’ve personally seen four ball calls that were upheld by a margin within 0.1”. In one game, there were two challenges in which the ball missed the zone by less than 0.1”.
As a catcher, Castillo has seen both sides of the challenge system. Most of his experience with ABS comes from behind the plate.
Castillo believes in using those challenges strategically, believing there are too many challenges in the Arizona Fall League. In the game before I talked to him, there were two upheld calls in which the margin was more than 2”.
“I feel like the best time we use is when the game is close or something like that. Don’t you think that’s a strikeout pitch? But, you don’t need to use it all the time or all the calls or something like that.”
The One-Knee Down Stance
In recent years, catchers have adopted the one-knee-down stance. Every professional catcher, including Castillo, uses this stance for good reasons.
“It’s more comfortable. It’s more flexible when you’re catching. You feel like you can move better when you’re catching. I catch it too with the [both knees] up, but sometimes it’s really hard for your movement from side to side.”
There are clear benefits beyond lateral movement with the one-knee down stance. It saves wear and tear on the catcher’s knees over the course of the season. That could theoretically allow for a team’s primary starting catcher to hold up better over the course of a season. That could mean more starts or a more consistent performance.
MLB’s Mike Petriello published a feature on this stance on July 1st. The article highlighted that the stance resulted in no negative impact on blocking or throwing out basestealers. The reduced wear plus potential for better framing, albeit that element will be less important with ABS, will likely result in a wider adoption of the stance.