Can Joe Boyle replace Shane Baz in the rotation?

The Rays will be looking to replace Shane Baz’s production in the rotation, and I think the Rays should look in-house and give Joe Boyle an extended run.

Boyle has always had plus stuff, but he’s had trouble sticking in the major leagues in previous seasons due to his lack of both control (the ability to throw strikes) and command (the ability to place the ball where he wants to); however, during his first full season in the Rays system, he’s meaningfully improved both of those skills. And, maybe most impressively, Boyle has made these strides while learning a new off-speed pitch. Those off-speed pitch types — changeups and splitters — are generally more difficult to both control and command, so the fact that he has improved in these areas while implementing the new pitch is a reason to be excited for the future.

There are several ways to evaluate control and command.

Control is defined as the ability to throw within and around the zone. This can generally be measured in strike rates and zone rates, but Command is the ability to throw a given pitch to a specific location, and it’s a little more tricky to quantify. Heat maps are a popular way to visualize command — if a pitcher is landing most of his pitches in a single specific spot or two, it’s an indication that he’s commanding the pitch — and I’ve created a metric that I’m calling “Command Deltas” to help measure it in a more numerical sense.

I’m not the first person to experiment with Command Deltas (Kyle Snyder has mentioned it a few times in various interviews throughout his time with the Rays), but I think I’ve landed on a relatively simple yet powerful version of the concept that I’m excited to share.

Above is a chart depicting Boyle’s combined Strike% and Zone% for his arsenal at both the Triple-A and MLB levels for his career. Note that he’s shown sustained improvement to his Strike% beginning in March of 2025, the result of adjustments that probably were initiated in December 2024 when he was first acquired. But even more telling than the Strike%, which includes pitches out of the zone that batters swung at (which can be inflated for pitchers with great stuff facing overmatched minor league batters), is looking closely at the Zone%.

Joe Boyle finished the 2025 season with three consecutive months of zone rates above 50%. The Major League average Zone% is typically 49-50% each year. The important thing here is the trend, more than the exact numbers, and he steadily increased his percentage of pitches inside the zone throughout the 2025 season, finishing with three consecutive months above the average. Meanwhile, the usage on his off-speed pitch went from 10.8% in March through May to 15.9% in August through September, showing that the improved command isn’t coming cheaply by spamming fastballs. He achieved the highest sustained Zone% of his career while also leaning further into his new off-speed offering.

Joe Boyle has always shown the ability to generate whiffs, running an 80th percentile whiff rate for his MLB career compared to pitchers with at least 2000 pitches thrown since 2023. He’s also shown some ability to limit hard contact (a more slippery concept to define, but an 80th percentile barrel rate over the same period). So the missing piece he needs to reach a new level is the ability to stay in the zone so his plus stuff can play.

Below are Boyle’s heat maps from 2024 (top) and 2025 (bottom). While we can compare the two sets of heat maps visually to evaluate changes in intention and execution, quantifying the growth with Command Deltas across both seasons really emphasizes how far he’s come.

First, looking at his fastball locations, we can see a concerted effort to locate up and arm-side, where its movement naturally takes it. His cut-slider locations have tightened, living mostly in the zone (possibly too much?) while those that were off the plate tended to be slightly down and armside — a desirable location for a breaking ball. His splitter is a work in progress and looks a bit scattershot, but we can see that it’s been thrown in the zone, and also far below it.

So, how do we quantify that growth?

Here’s a brief rundown of how I calculate Command Deltas (here’s a more detailed explanation and a link to the leaderboards I’ve created):

Note that this methodology can struggle to rate pitchers who change their intended location for a pitch. If a pitch is thrown intentionally to more locations in year two as part of a pitching plan, it may look to the metric like the pitcher’s command has deteriorated, even if it has not. Our visual inspection suggests this is not a complication we need to worry about with Joe Boyle.

Below are Boyle’s Command Deltas from 2024 and 2025:

Boyle has improved his four-seamer command from far-below-average to simply below-average, and his slider command has improved from below-average to average. His splitter command was well-below-average, but because that was a new pitch for him it’s reasonable to hope for continued improvement in 2026.

A realistic outcome for Boyle’s command in 2026 would look something like what Hunter Greene did over the last few years. They’re both big RHP with similar arsenals, but Greene is more advanced with his command at this point. Similar to Boyle’s journey, in 2024 Greene began throwing a splitter, and had 40 grade command of it to pair with average command of both his fastball and slider. Then in 2025, Greene took a step forward and showed above average command of his fastball, average command with his slider, and fringe-average command with his splitter. This resulted in Greene’s best walk rate of his career last season, and it looks sustainable. I could see Boyle take a step forward with potentially his slider leading the way because he has the best feel for it along with average command of his fastball and fringy command of his splitter.

Over the full course of the 2025 season, Boyle displayed average control, and below average command, both of which were improvements from 2024. The fact that he ended the seasons with his longest sustained run of quality locations suggests meaningful growth. His overall command grades align more with a reliever profile than a starter, but his lack of consistency with his mechanics and shapes prior to joining the Rays combined with the steady improvement he showed in his first season with Tampa Bay suggest that he still has potential as a starter worth checking on.

Boyle was something of a blank slate heading into 2025; he has a foundation to build on for 2026.

I wonder what it would look like if Boyle leaned into throwing his slider more. He has the best feel for it among his three pitches, and its cutter-ish shape and 90+ mph velocity means it should play well against both sides of the plate.

His fastball shape also changed in 2025 upon joining the Rays, losing some vertical rise and gaining some armside run. This is likely the result of him continuing to drop his arm slot to a more natural throwing motion for him — in 2025 it sat at 32°, down from 48° the year before and 53° in 2023. This is a significant change, and I think another year of consistency with these new mechanics should lead to improved command of his fastball.

The splitter is a wildcard for sure, but the fact that it was an offering he could throw ~15% at the Major League level is encouraging, and he should continue to find more command with more reps. Even getting to just average control and command across the board like Greene did in 2025 would make Boyle at least a mid-rotation type of starter given his overpowering arsenal.

I’m hoping to see continued improvement from Boyle in year two with the Rays. Three plus pitches, a career high workload, and budding command all bode well for him in 2026.