The past five years
That sinking feeling
Cahill definitely had a disappointing 2013. Coming in with a career ERA+ to that point of 107, a figure roughly matched during his first season with the Diamondbacks (108), he put up an ERA+ last year of just 96: So, what changed for Trevor? The one thing we can't blame is "luck," with an identical BABIP for both seasons of .295. virtually at the MLB average of .297. However, the main cause seemed to be significantly better contact being made by opposing hitters. Cahill's line-drive percentage for 2012 was a very respectable 14%, but ballooned all the way up to 22% in 2013.
That's interesting, because normally, such a drastic change in line-drive rate would lead to an increase for batting average on balls in play - line-drives are much more likely to be hits that fly- or ground-balls. [Last year across all of MLB, about two-thirds of line-drives became hits, compared to one-quarter of ground-balls, and less than one-tenth of fly-balls] However, for Cahill, the increase in the raw amount of line-drives was countered by a lower BA for other balls in play.. In particular, his BABIP for fly-balls was a mere .049, barely half the MLB average (.095). Those are likely to regress to the mean in 2014, so the same number of line-drives could spell trouble.
It wasn't that hitters were being particularly aggressive. Indeed, this year, the percentage of times they swung at his offerings decreased by a small amount, dropping from 41.9% to 41.1%. However, that overall number conceals a split: it was powered entirely by a sharp decrease in swings at pitches out of the zone, from 29.5% to 26.9%, in the zone, hitters actually swung more often, increasing from 57.3% to 59.1%. And when they swung, they didn't miss as much, in or out of the zone: 18.5% of the time, down from 22.2%. It looks like Cahill's pitches weren't fooling as many batters in 2013 as they had done in 2012, with his K-rate down and the walk-rate up.
It's certainly true that his overall numbers were impacted by his wretched June: over those six starts, he went 0-5 with a 9.85 ERA and a line against of .364/.435/.598. A six-week trip to the DL followed, though that should carry forward, the result of a freak injury after he was hit on the hip by a comebacker - his first DL stint since the beginning of the 2010 campaign. However, Cahill's struggles were already pronounced at the time of that incident, having allowed 15 earned runs over the 14.2 prior innings. But, for whatever reason, the time off seemed to do the trick, and Trevor pitched much better after his return, with a 2.70 ERA during his final nine appearances of the season.
So, there's some evidence in both directions here. Optimists can say, "If he just avoids that sucky June, he'll have an ERA around three." Pessimists can point to the decline in Cahill's peripherals, and worry that, at the grand old age of 25 (he turns 26 on the first of next month), his best days are already behind him. Regardless, he's under full team control for the next two seasons, at a total cost of about four million dollars less than Bronson Arroyo. Put that way, it doesn't seem so bad, does it? But if the Diamondbacks are to exercise the team options for 2016 and 2017, they will probably want more out of Trevor than they saw last season.
This article is part of our 2014 Diamondbacks expectations series - check out the other entries. As we go through spring, we'll have a series of pieces looking at each of the players likely to be on the 25-man roster for the home opener. It's an open forum, to discuss expectations, hopes, fears and their potential contribution to the 2014 season.