Quick look: Taijuan Walker's fastball and new mechanics

After his disastrous start on Saturday against the Angels, Ryan Divish reported that Taijuan Walker stayed late at the field working with pitching coach Mel Stottlemyre to figure out what went wrong. The next day, Shannon Drayer reported that he and Stottlemyre were at it again, this time adjusting his mechanics. For a player who has been criticized for his effort and grit, it was a good sign to see Taijuan seeking help from the team.

After just one start with his new mechanics, it’s way too early to jump to any conclusions. By my eye (and confirmed by Nathan and John), he looked a bit uncomfortable on the mound. His throwing motion looked a bit more compact with a smaller leg kick. Thanks to the indomitable Jose, here’s a side-by-side GIF comparing pitches from his last two starts (9/3 on the right, 9/8 on the left):

There was one statistical oddity that I noticed about his fastball that I wanted to check in on. In a post on RotoGraphs yesterday (posted before the Mariners started their game), Jeff Zimmerman briefly took a look at fastball spin rate as an injury indicator. His data indicated that Taijuan had lost more than 100 RPMs off his fastball’s average spin rate in his start on Saturday. I fired up Baseball Savant to see if this was a trend and if the new mechanics had any positive effect on the pitch.

Here’s a graph of Taijuan’s average spin rate and average velocity on his fastball from each of his starts this year:

Towards the end of August, we see a precipitous drop in average spin rate compared to his season average (2,115 RPM), culminating with a season low on Saturday. Those other valleys in the graph correspond to the foot issues he was having earlier this year.

On a fastball, higher spin rates usually lead to greater "rise" on the pitch while a low spin fastball has more drop to it. And looking at the PITCHf/x data, there's a corresponding trend in his average vertical movement. Here are the relevant data points for his fastball from his four starts since returning from Triple-A:

As you can see, Taijuan's fastball had the lowest amount of "rise" to it last night and it's been well below his season average in all four starts. There also aren't any significant changes in the pitch's characteristics appearing in the data from the new mechanics that were debuted last night. In practice, he was able to generate just four swinging strikes (6.9%) with his fastball last night and allowed nine balls in play (15.5%) off the pitch.

A slower, straighter fastball is not exactly an improvement to Taijuan's repertoire. The worse-case scenario is an injury—perhaps a recurrence of his foot problems—that has seriously hurt his effectiveness. Of course, any mid-season mechanical changes should take lots of time and repetition to have any benefit. Hopefully, Taijuan and the team have an offseason plan to evaluate and assess their effectiveness. Until then, he'll be working through these adjustments on the fly against major league batters while the team clings to a sliver of playoff hopes.