Can Trevor Cahill Improve Again?

Trevor Cahill has come a long way in four seasons. After a questionable performance during his rookie year, Cahill has steadily improved over his career. His WAR reflects this too, as it’s risen from 0.6 to 3.4 over the last four seasons. A decent chunk of that improvement can be tied to Cahill’s strikeout rate, which has also steadily risen over his career. While Cahill has been around for what seems like a long time, he’s still young, not turning 25 until March. Because of that, it’s still plausible to think there’s a chance for Cahill to get even better.

Strikeout rate isn’t the only factor driving Cahill’s improvement over his career, but it is significant. Cahill looked like a below-average strikeout pitcher during his first season, but last season he flashed the ability to strike out hitters at an above-average rate. His K% over that period rose from 11.6 to 18.6. Have we ever seen that type of improvement before?

From 1969 to 2012, there were 27 pitchers who had a strikeout rate of at least 12.6 percent during their age-21 season, including Cahill. First, let’s look at whether any pitcher on the list was able to increase their K% as much as Cahill during their first four seasons in the league. After a number of players were eliminated for either not meeting age limits, or not pitching enough innings at age-24, we are left with this list.

Name	Age-21 K%	Age-24 K%	Difference
Trevor Cahill	11.6	18.6	7
Mike Witt	11.4	17.2	5.8
Clay Kirby	12.1	17.4	5.3
Dave Rozema	6.7	11	4.3
Ross Grimsley	10.2	13.2	3
Dave Stieb	9.2	11.9	2.7
Jim Slaton	10	11.8	1.8
Richard Dotson	12.6	13.7	1.1
Steve Trout	11.2	11.6	0.4
Jon Garland	12	12.2	0.2
Dan Petry	12.3	10.9	-1.4
John Mitchell	11.6	8.5	-3.1
Lary Sorensen	9.6	6.4	-3.2
Doyle Alexander	11.6	8.2	-3.4

Of the 14 players who still meet our requirements, Cahill has seen the larger gain in his strikeout rate. Mike Witt, Clay Kirby and Dave Rozema also deserve some credit, as they showed significant improvement as well. Going forward, did any of these players continue to improve their strikeout rate, or were they done developing in that area by age-24?

Name	Age-24 K%	Age-25 to 30 K%	Difference
Dave Stieb	11.9	16	4.1
Lary Sorensen	6.4	8.1	1.7
Dan Petry	10.9	12.5	1.6
Doyle Alexander	8.2	9.7	1.5
Jon Garland	12.2	12.5	0.3
Jim Slaton	11.8	10.5	-1.3
Mike Witt	17.2	15.6	-1.6
Richard Dotson	13.7	11.7	-2
Steve Trout	11.6	9.4	-2.2
Clay Kirby	17.4	14.4	-3
Ross Grimsley	13.2	7.3	-5.9

Moving forward, only one pitcher saw a big improvement from age-25 on, Dave Stieb. Stieb experienced a smaller improvement from age-21 to age-24, but then saw a Cahill-like jump going forward. He and Jon Garland are actually the only two guys who saw improvement during both stages of their careers, and Garland barely improved both times. Witt, Kirby and Rozema, who were close to Cahill on the first list, all saw regression. Rozema didn’t even pitch enough to qualify for the second list, while Kirby and Rozema failed to improve any further.

It’s pretty rare for Cahill to have already shown this much improvement with his strikeout rate. And going forward, it’s going to be even more difficult for him to improve any more. If that second list shows us anything, Cahill has an equal chance of treading water, and losing some of his gains moving forward. The fact that Cahill has seen the larger surge in his strikeout rate could actually provide some hope, though. There’s been nothing fluky about his improvement to this point in his career, so there’s no major reason to expect him to drop off completely. That said, it would be incredibly rare for Cahill to see another surge in his strikeout rate. It’s happened before, but not often, and not to the same extent that Cahill has already improved. If he hopes to improve again, he’ll have to continue to defy the odds.