JJ Wetherholt Had a Rookie Season for the Ages. So Why Did His Bat Fade?

JJ Wetherholt did what so few Cardinals rookies have done in recent years: lived up to the hype. He provided average offense, brilliant defense, and excellent baserunning on his way to the best rookie performance we have seen in St. Louis since Albert Pujols. The season was an unqualified success, but there is still plenty to dissect, particularly on the hitting side of JJ’s game. As I started looking at his season, there were several overlapping topics I wanted to dig into. The result of this digging is a somewhat meandering, but hopefully interesting, deep dive on a handful of questions that I couldn’t live without trying to answer. 

How bad was the second half? 

Through June 22, Wetherholt had compiled a 126 wRC+ and was on pace for a 7-WAR season. From June 23 on, he slumped to a 73 wRC+ to pull his season offensive line down to basically average. This is an arbitrary date, but it gives us a good jumping-off point to start looking for clues as to what changed. It is important to note that Wetherholt’s expected production (xwOBA) dropped from .359 to .333, which was not nearly as dramatic a drop as his actual production. Converted to wRC+, the drop-off would have been 127 to 109. There was clearly some bad luck involved with Wetherholt’s second-half swoon, but some real regression as well. 

First, let’s check on JJ’s plate approach. He maintained basically the same walk rate throughout the year (10.7% to 10.0%), but his strikeout rate did tick up slightly from 15.5% to 18.2%. His underlying metrics shifted a bit as well.

Wetherholt actually improved his elite chase rate during the second half of the year, ranking behind only Steven Kwan and Geraldo Perdomo in all of baseball from June 23 on. The flip side of this was that his Swing% on pitches in the zone fell from 65% to 60%. That is not necessarily the end of the world, but his more passive approach did lead to a few more strikeouts, despite the improved contact rate. His overall Swing% dropped 3.3 percentage points even as pitchers threw him more pitches in the zone in the second half (49% to 51.5% Zone%). 

There is nothing alarming about his slight change in plate approach, but we will file away the reduced aggression as something to keep an eye on as we go deeper. 

A bigger concern is that Wetherholt’s isolated slugging percentage dropped from .157 to an anemic .086. Let’s flip over to some Statcast metrics to see if we can find clues on the missing power.

Wetherholt’s exit velocity (EV) and 90th-percentile exit velocity (EV90) dropped around 1 mph each in the second half. To contextualize this lost thump, I looked at all players with at least 200 plate appearances in each half of the season and calculated the change in EV and EV90 between halves. Across this pool, the standard deviation of the change was 1.6 mph for EV and 1.1 mph for EV90. Given Wetherholt’s identical Barrel% in each half and his improved HardHit%, these downticks are not overly concerning. 

The change in launch angle is more dramatic. The six degrees lost on launch angle (a two-standard-deviation change) was the fourth-biggest drop in baseball and led to Wetherholt’s ground-ball rate increasing from 40% to 50%. Let’s see if his opponents did anything differently in the second half. 

How did pitchers change their plan of attack? 

Right-handers relied on the four-seam fastball around 32% of the time against Wetherholt, which was consistent in both halves. Wetherholt feasted on these pitches in the first half, cranking out a .451 wOBA. In the second half, his collective opponents made a couple of adjustments. First, they reduced the percentage of four-seamers in the zone from 60% to 54%. Second, they started attacking Wetherholt inside more aggressively. The share of fastballs on the inside and inside off the plate increased from 26% to 35%. The tactic seemed to work, as Wetherholt’s wOBA against four-seamers fell to a more human .363. Righties also switched from cutters to sinkers to combat Wetherholt in the second half. Cutter usage fell from 10% to 5% while sinker usage increased from 12% to 20%. This change could have hurt Wetherholt’s ability to drive the ball in the air. His average launch angle against right-handed sinkers for the year was -0.2 degrees compared to 18.2 degrees against four-seamers and cutters. 

Lefties followed a similar pattern to their right-handed counterparts when it came to attacking Wetherholt. They increased the share of pitches thrown inside by about 5 percentage points. Also similar to righties, sinker utilization increased dramatically in the second half, going from 27% to 35%. Another change that caught my eye was that lefties reduced their usage of breaking pitches against Wetherholt in the second half, going from 39.5% to 32%. While Wetherholt didn’t do eye-popping damage against lefty breakers, he had an absurdly low 18.5% chase rate against those pitches on the season. It seems that his left-handed opponents grew tired of watching him spit on pitches off the plate and resorted to a steady diet of fastballs. 

How big of an impact did the wrist injury have? 

Wetherholt went on the IL at the end of August but had reportedly been dealing with pain in his wrist for about a month. His bat-tracking metrics also changed, perhaps as a result of injury or fatigue. 

This 1.2 mph drop doesn’t sound like much, but because of the wrist issue, I took a deeper look. Wetherholt’s first-half bat speed was in the 52nd percentile while his second-half bat speed dropped to the 34th percentile. Bat speed is an extremely stable statistic. In fact, this drop of 1.2 mph was the largest in baseball this season between the first and second halves. I don’t think we can say that this change caused Wetherholt’s regression; there are plenty of great hitters with slower bat speed. But it is pretty clear evidence that something changed. Here is a zoomed-in version of Wetherholt’s bat speed over the course of the season.

It seems like a safe assumption that the change in bat speed was related to the wrist injury, but perhaps attack direction gives us a hint of the secondary or related effects of the issue. Attack direction measures the direction the sweet spot is moving at contact. Wetherholt’s average angle was 4 degrees to the left-center gap in the first half and jumped to 9 degrees in the second half. Whether by design or not, Wetherholt dramatically shifted to a more opposite-field approach in the second half. This was the second-largest shift in baseball half-over-half. Side note: Alec Burleson had one of the biggest shifts in baseball in the other direction, getting more pull-heavy. 

This change in attack direction dropped Wetherholt’s pull rate from 41% to 34%. His percentage of balls pulled in the air dropped from 15% to 10%. Unless you are James Wood or Fernando Tatis Jr., it is tough to produce power consistently without lifting the ball to the pull side. The lack of pull power could be as simple as Wetherholt being a tick late on pitches because of fatigue or the wrist injury. He also could have tried to compensate for his reduced physical capabilities by going with a more all-fields approach. Or it could have been something completely different! We know Wetherholt focuses on driving the ball to left field. But the combination of pitchers coming inside more frequently and Wetherholt taking a more opposite-field approach does not seem like an intentional strategy. 

Why the gap between expected and actual results? 

The last mini-topic I want to tackle is the gap between Wetherholt’s expected and actual production. On the season, his wOBA was .318 compared to his xwOBA of .347. Had he matched his expected output, his season wRC+ would have risen from 101 to 118. Interestingly, the Steamer system has Wetherholt projected for a 118 wRC+ next season as well. His fWAR would have been right around 6 instead of the 4.6 he actually posted. 

Before we start counting our wOBA chickens, we need to take a closer look at Wetherholt’s batted-ball profile. xwOBA is calculated using launch speed and launch angle, but it does not take into account the direction the ball is hit. That means the statistic underrates players who pull the ball to the shorter parts of the field and overrates players who hit a higher proportion of balls to center. In case you are interested in an eye chart quantifying what this actually means, here are the results across MLB for 2026.

All fly balls hit to center field in 2026 had an xwOBA of .445, but the actual wOBA was only .284. The gap is offset by pulled fly balls outperforming expected results by .261. I also highlighted opposite-field ground balls, as they have the third-largest delta between expected and actual outcomes. 

Here is how Wetherholt compares to the league-average distribution of batted-ball types. 

Based on his batted-ball profile, Wetherholt is definitely overrated by xwOBA. He hits more fly balls to center, fewer fly balls to his pull side, and fewer opposite-field ground balls than the league average. This doesn’t mean that he is a bad hitter; it just means that the way xwOBA is calculated overstates how good he is. The final question this leaves us with is how much it overstates his deserved results. To answer this question, I recalculated xwOBA for all batted-ball events by applying the difference between expected and actual wOBA for each hit type. So, if Wetherholt hit a fly ball to center with an xwOBA of .361, it would be adjusted down to .200 to capture the real-world difference in results. As you would hope, this new metric shows Isaac Paredes as the biggest gainer, going from an xwOBA of .323 to .345. Nolan Arenado ranks as the fourth-biggest gainer, by .017. 

As expected, Wetherholt’s xwOBA does drop a bit from .347 to .339. Not too big a penalty. This would have given him a “deserved” wRC+ of 113 and WAR of 5.6. That is a pretty good player right there. 

The Verdict

Did I answer the questions I set out to? Kind of. It is incredibly difficult to attribute changes in performance to a specific injury, but I will be keeping an eye on Wetherholt’s bat speed and pull rates early next year to see which direction things trend. I also think he will need to make some adjustments. He doesn’t need to become a left-handed Arenado, but he needs to find a way to pull the ball with authority more frequently and combat the barrage of sinkers his opponents attacked him with in the second half. Most encouraging is that even with the banged-up second half, he was still an excellent player. Looking deeper at his batted-ball profile convinced me that he was also extremely unlucky, even if he wasn’t quite as unlucky as his expected stats would lead you to believe. Wetherholt may not take home a Rookie of the Year trophy, but he looks like an MVP candidate to me as early as next season.