We had a pretty good idea of who Trevor Cahill was: owner of a career 4.13/4.27 ERA/FIP, back-end starter, ground ball pitcher. He lost his rotation spot while pitching for the Diamondbacks in 2014. During 2015, he was released by the Braves after a failed transition to the bullpen, and, after opting-out of a minor league contract with the Dodgers, there was the possibility that this might be the end of any meaningful career for him. Still only 27 years old, he wouldn’t have been the first fringy starter to flame out of the league.
In late August, however, he signed a minor league deal with the Cubs, and two weeks later they called him up to the major league bullpen. Something pretty drastic had happened over the course of his time in the bullpens of the three teams he was employed by during 2015, and it all seemed to culminate in his 17 September and October innings for Chicago: he posted a stellar 27% K-BB% during that stretch, returning successfully to his ground ball ways (61.8%) and a 2.12/3.13 ERA/FIP.
Those 17 innings were, of course, a tiny sample size. But in those innings, as well as his successful work during the playoffs, we glimpsed who the new Cahill might be, and it was the pitcher the Cubs think they just signed to a low-risk, one-year, $4.25 million deal last week.
First, we saw a big velocity jump from Cahill in 2015. He almost exclusively throws a sinker as his main fastball, and he increased its velocity in 2015 by about two and a half mph from its highest point in 2014. Take a velocity look at a chart for his sinker for the months of 2014 and 2015, courtesy of Brooks Baseball:

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