Alejandro Kirk’s Slugging Conundrum

Something weird is happening with Alejandro Kirk. It’s not that he’s having a great season. That’s not weird at all. Kirk ranks third among catchers with 2.4 WAR and 21st among all players. He’s also hitting much better than he has in the past two seasons, but that’s not necessarily weird either. After combining for a wRC+ of 95 in 2023 and 2024, Kirk has a 129 wRC+ this season, the same as he ran in 2022, when he was an All-Star and won the Silver Slugger. He’s always been great with the glove, and it now looks like his bat is back. His .370 xwOBA and 119 DRC+ are also his best since 2022.

What’s weird is that he’s hitting the ball harder – much, much harder – but he’s not necessarily hitting for more power. Let me show you what I mean with a table. Below are a bunch of contact-quality metrics for the five full seasons of Kirk’s career. On the far right is his isolated power. Usually, contact quality and power are pretty much synonymous. If you hit the ball hard, you’re going to end up with doubles, triples, and homers. Usually.

This season, Kirk is running the highest average exit velocity, 90th percentile exit velocity, hard-hit rate, and slugging percentage of his entire career, and not by a little bit. These are huge jumps. Everyone’s favorite 5’8” catcher is in the 97th percentile in hard-hit rate! Yet his ISO is merely the third best of his career, a mere nine points above last season’s mark. I’m curious about why Kirk is hitting the ball so much harder all of a sudden, and I’m curious about why it’s not resulting in a massive power spike.

Let’s start with who Kirk is as a hitter, because he’s awfully fun. Over the past three seasons, his contact and strikeout rates have never dropped below the 92nd percentile. He’s an excellent contact hitter who puts up solid exit velocities, takes his walks, and never strikes out. This season, however, Kirk looks quite different. We know he’s hitting the ball harder, and that’s no accident. As many have noted, he’s swinging much harder too. His average bat speed has gone from 70.1 mph in 2024 to 72.3 mph this season, and that’s true any way you slice it. You can look at Kirk’s bat-speed splits in terms of contact quality, pitch types, or locations; no matter the situation, he’s always swinging harder this season.

As you might expect from a player who’s swinging so much harder, he’s also just more aggressive in general, resulting in the highest swing rate of his entire career and an increased whiff rate. But that increased whiff rate is still only 19.3%, which puts him in the 81st percentile and means that if he swings five times, he’s probably only missing once. That aggression also means his called strike rate has fallen to a career low, and he is also seeing more pitches in the zone this season. Put it together, and even with the increased aggression, Kirk is harder than ever to strike out. Not only is he not striking out much, but he’s also batting a league-best .346 with two strikes. (Even more interestingly, his 71.6-mph bat speed with two strikes indicates he’s not dialing back much; he’s just hitting the ball really well.)

As a result, Kirk is posting the lowest walk and strikeout rates since his rookie season, and he’s putting the ball in play in a career-high 83.5% of his plate appearances. His walk rate is 3.2 percentage points below his career rate, and his strikeout percentage is 1.4 points below his career mark. That means 1.8% of the time, Kirk is trading a walk for a ball in play. In isolation, that’s not a great trade-off. Walks have a .694 wOBA, and even Aaron Judge doesn’t get that much production when he puts the ball in play (although at .685, he’s insanely close; we’ll talk about that tomorrow). But the trade-off has worked out just fine for Kirk, because all that power has allowed him to be better than ever in the larger portion of the time that he does put the ball in play. His .369 wOBACON and .390 xwOBACON are the best of his career.

Knowing all that, let’s get back to our main question. Kirk has been better than ever when he puts the ball in play, with a .341 BABIP that’s miles above his .286 career rate. His batting average is actually 13 points higher than his expected batting average, the biggest differential of his career, but his slugging percentage is 62 points lower than his expected slugging percentage, the biggest differential of his career in the other direction. Why hasn’t that power translated into extra bases more often? I’m sure part of it is that Kirk is a slow catcher who gets held to singles on balls that would be doubles for other players. But I don’t think that’s the whole story, so I hauled in the usual suspects. It’s not because he’s no longer lifting the ball. In fact, he’s putting more balls in the air than he has in any season since 2021. Same with lifting the ball to the pull side. But take a look at the stats below, which show his performance on hard-hit fly balls and line drives.

This season, when Kirk hits the ball hard and in the air, he’s underperforming his xwOBA by 175 points. That’s nowhere near the biggest gap in the league, but it does put Kirk third-to-last in baseball in wOBA on hard-hit air balls. These are the most valuable balls a hitter can hit, but Kirk isn’t being rewarded for them as we’d expect, even though he’s pulling them more often than ever.

We’re about to put all the puzzle pieces together here, and the trick is that looking at hard-hit balls isn’t enough. The cutoff for hard-hit balls is 95 mph, but if we increase our threshold to 100 mph, we zero in on balls that are likeliest to go for home runs. This season, when Kirk hits a ball in the air over 100 mph, he hits it to center field 56.3% of the time. Over the previous four seasons, that number was 38.7%. That’s a big jump. When he hits the ball hardest, Kirk is hitting it to the big part of the ballpark, where it’s most likely to end up as an out. Below you can see the heat maps of Kirk’s hard-hit balls over the past four seasons. This year, there’s a lot more red right up the middle. There’s almost none in the corners, where Kirk has traditionally hit all his home runs, and there’s almost none in the gaps.

This could just be a bit of randomness. We’re only a third of the way through the season, and Kirk is smashing offspeed stuff in particular. Usually, players pull offspeed stuff when they hit it really hard, because its slower velocity means their bat meets it farther out in front. This season, the league has a 54% pull rate on hard-hit offspeed pitches. Maybe this will all balance out. However, this could also be a function of Kirk’s more aggressive approach.

As you can see from the spray charts above, when he hit the ball hard in previous seasons, he was very likely to go to the opposite field. Like many contact gurus, his swing was geared to meet the ball deep and drive it the other way. Now, he’s opened his stance by a few degrees. He’s swinging harder and meeting the ball farther out in front; his average intercept point is 1.7 inches farther ahead of him than it was over the last two seasons. That’s not enough to start pulling the ball all the time, but it could be enough to turn some of that opposite-field contact into straightaway contact. Kirk is a hybrid player now, swinging hard and hitting the ball hard, but still making a lot of contact and squaring the ball up harder than ever. His batted balls seem to be caught in between as well. He’s still hitting better than he has in years, so it’s not as if this is a problem that needs to be fixed. But it might mean Kirk’s power output continues to lag behind his actual power.