His groundball rate is at its lowest rate ever
One thing that hasn't helped AJ's cause has been a pretty significant drop-off in his groundball rate. Over the last three seasons, AJ's groundball rates have been 50%, 47.9%, and 39.6%. Aside from the fact that a deeper look into WHY his groundball rates have steadily decreased is probably needed, that brings us to this season where his groundball rate currently sits at 29.2% which is shockingly low for him.
This certainly hasn't helped his BABIP numbers as soft line drives are significantly more likely to be productive than groundballs. With a career high line drive percentage at 35.4% in 2023, that is a problem. It certainly isn't the only problem, but he really needs to put the ball on the ground more.
His expected stats are trending in the wrong direction
One thing that we have made sure to mention when talking about AJ is that a lot of his peripherals are, in general, good and that remains true. His whiff rate and chase rate are still elite and the expected stats against him still look pretty good. On the surface, he still profiles as a good to great reliever if you ignore the results.
However, they ARE worse than they were the last few seasons as his expected batting average against (.239), expected slugging against (.401), and expected WOBA (.307) are his worst marks in the categories since 2019 which is not great news. There isn't one pitch that has been the culprit, either, as his fastball, cutter, and changeup have all seen significant declines in their expected stats over last season's numbers. Some of that is explained by the aforementioned bad luck, but not all of it. Maybe he is tipping his pitches? Maybe the new pitch clock is taking its toll? Regardless of the cause, the symptoms are not ideal.
His fastball isn't putting guys away
While all of his pitches have seen declines, his most used weapon has arguably declined the most and that is his fastball. The average velocity of the pitch is down from 96.6 mph in 2022 to 95.7 mph in 2023 and the horizontal break on it is down an inch as well (although it is getting 0.5 inches more vertical movement over the average from last year).
The end result has been that guys are hitting .269 and slugging .462 off of his fastball in 2023. Last season, AJ's four-seam was his best pitch in terms of run value as it saved 12 runs in 2022. In 2023, it has been a net negative and profiles more similarly to when it was at it worst when it had a run value of 10 in the wrong direction back in 2019.