First four starts: 6.00 ERA, 12/11 K/BB in 21 innings, 90 mph exit velocity
Last five starts: 2.67 ERA, 43/5 K/BB in 30 1/3 innings, 83.2 mph exit velocity
That's not just a small change; that's an enormous change, particularly when it comes to strikeouts. Look where Wood, who faces Jason Hammel and the Cubs on Monday after being pushed back from his scheduled Friday start due to a sore triceps, ranks in strikeout percentage among all big leaguers over the last 30 days, per FanGraphs:
Top strikeout rates, past 30 days
1. Jose Fernandez, 39.7 percent
2. Clayton Kershaw, 38.5 percent
3. Wood, 37.0 percent
4. Max Scherzer, 36.6 percent
5. Stephen Strasburg, 31.7 percent
Now, without question, we're dealing with small samples, and just about anything can happen in a few starts. Yet even accepting that truth, piling up 43 strikeouts against only five walks, immediately after having basically a one-to-one ratio for the first month of the season, seems impossible to do by accident. You can't strike out hitters at a higher rate than Strasburg (or Noah Syndergaard or Jake Arrieta or Chris Sale, and on and on) for any period of time just by luck.
So what changed? Back in late April, Wood told MLB.com that he'd made a mechanical adjustment that he'd felt had begun to show results in his April 30 start, against San Diego. Wood carried a 6.00 ERA into that start, and his funky delivery has been the cause of ever-present mechanical work for his entire career, so at the time the claim didn't really open that many eyes.
That timing isn't just a coincidence, though, and the evidence does point to that change being largely responsible for his success of late. Wood referred to the change in foot stride as the "last piece of the puzzle" to get his consistency back, and that's both good news and bad.
Although it's nearly impossible to see the change Wood mentioned on video, and although it hasn't resulted in a change to his extension, the difference is extremely clear when you look at his release point. Compare, for example, April 19 against the Braves and May 15 against the Cardinals, from FanGraphs:
What you should be noticing is that in the Cardinals game, Wood's release point was tightly clustered. There was almost no noticeable difference between his two primary pitches, a sinking fastball and a knuckle-curve. But in the earlier game, you can clearly see that the fastball came out several inches -- in some cases more than half a foot -- differently from the breaking ball. Whether that was a tipoff to opposing hitters or just difficult for Wood to maintain command with multiple release points, or both, it's a small change that has a big impact.
So why is that potentially a concern? Because "minor tweaks" may as well be Wood's nickname. Thanks to his notoriously unorthodox delivery, it seems he is always working on something. Here's a story from 2015 in which Wood is described as "piecing it together," and another about changing his mound position. Earlier that year, it was "making adjustments." Last offseason, we pointed to him (along with Rick Porcello) as a Statcast™ rebound candidate, in part because of all the offseason video work he'd done on his mechanics to change his arm angle.
All of which is to say: Wood is extremely talented, as he's shown over the past month and earlier in his career, and for as long as he can keep his mechanics consistent, he can be a worthy partner to Kershaw and Kenta Maeda. It's the consistency that's the problem, however. It always is.