How Mariners' aging ace Luis Castillo is brilliantly defying Father Time

Here's some advice for Seattle Mariners fans who want to remain confident in Luis Castillo: Whatever you do, don't go to his Baseball Savant page.

The first thing you'll see if you do go there — here's the link if you dare — is a whole lot of blue. Blue denotes metrics that are below average, and the 32-year-old righty is treading in that territory so far in 2025 with his whiff and strikeout rates, plus his average exit velocity and hard-hit percentage.

The one exception is his average fastball velocity, which is still better than most at 94.8 mph. But that is also nearly 3 mph below the 97.4 mph he averaged on his heater when he joined the Mariners in 2022, which made him one of the elite flamethrowers in Major League Baseball.

And yet, he's headed into his Sunday assignment against the Houston Astros with a 3.10 ERA to show for his first 10 starts. And how he's doing it makes no sense...in a good way.

Luis Castillo has thrown out the script for how to age gracefully

When a pitcher starts losing digits on the radar gun, it is typically a good idea to stop leaning so heavily on velocity to get by. Consider CC Sabathia, who went from being heavily reliant on his four-seamer to basically ditching it in favor of sinkers and cutters in the 2010s. As a result, he emerged from a dark period to finish his career on a relatively strong note.

We could argue about whether Castillo should be following the Sabathia playbook, but that would frankly be a waste of everyone's time. He's already made his decision to not just keep throwing fastballs, but to indeed throw more fastballs.

The three-time All-Star is throwing four-seamers and sinkers a career-high 67.4 percent of the time this season, and he is not exactly nibbling with all those heaters. He's throwing 55.2 percent of all his fastballs in the strike zone, the second-highest rate of his career after 2020.

Castillo's last start against the Chicago White Sox was the ultimate case of committing to the bit. Of the 94 pitches he threw over seven scoreless innings, 71 were fastballs. He even threw 27 straight at one point, apparently at the behest of Cal Raleigh.

“Cal said, ‘Let’s go for 50 today,’" Castillo said through interpreter Freddy Llanos, as per Bob Condotta of The Seattle Times. “I said, ‘All right, let’s do it.’ And when we were at the game we were at 27 [straight], and he asked me for a slider and I just kind of laughed at him and said, ‘All right, we’ll stay on 27.’ We didn’t quite get there."

Castillo already has a rich history of forcing teams to rewrite their scouting reports on him. To wit, he was initially big on his changeup and slider, until suddenly he wasn't. He seemed to get obsessed with vertical approach angle precisely when everyone else did, and the result was his four-seamer becoming one of the dominant pitches in baseball between 2022 and 2024.

He is still tinkering in 2025, only in ways that are more subtle. There actually is good stuff to find if you dig deeper into his Baseball Savant profile, such as how he's more short-armed with his delivery (i.e., less extension) than when he first arrived in Seattle. He's also getting more arm-side run on both his four-seamer and his sinker, the latter of which tops the charts in horizontal movement.

What his scary batted ball metrics obscure is how much contact off him is non-threatening. At 43.4 percent, his ground ball rate is the highest it's been since 2022. Batters are also pulling the ball just 35.3 percent of the time off him, the lowest of his career. Which is good, because pulled balls generally equal death. Hitters have a .712 OPS overall in 2025, but a .996 OPS when they pull the ball.

Whether all this can sustain a 3.20 ERA is a good question. It would be the third-lowest of his career, and there's an eerie amount of distance between his actual ERA and his expected ERA of 4.18.

Still, Castillo wouldn't be sticking with this approach if he was pitching for metrics. He's clearly out there pitching for results, and the feedback is clear: It's working.