Before you learned that the Phillies signed 36 year-old RHP Aaron Harang yesterday, it's very possible, if not probable even, that you were unaware that Harang was still a person who sought employ as a pitcher for MLB baseball teams. Additionally, you were also likely surprised to learn that Harang enjoyed, if not quite a renaissance, at least a substantial bounceback season for the Atlanta Braves in 2014.
Well, good for him, then, but baseball players experience significant fluctuations in results all the time, even over the course of an entire season. Most of the time, these inconsistencies in performance are best attributed to randomness. So, before declaring a single good season from a 35 year old pitcher an indisputable indication of future performance, we need to find a reason to believe that improvement wasn't noise.
Before we do that, let me make one thing clear: Aaron Harang had his best season, by most any measure, since 2007. He posted the lowest ERA (3.57) and FIP (3.57) of his career. You would have to go back to 2008 to find a better K% than his 2014 rate of 18.4%. He also pitched more innings (204.1) than he has since 2007, which has more value than people acknowledge given the scarcity of reliable back-end arms. Aaron Harang was a good pitcher in 2014, which, at this point, no one can take away from him.
But, whether Harang was effective in 2014 is a different question from whether we can expect him to continue to be good in 2015. To answer the latter question, we ultimately want to figure out whether his bounce-back 2014 was the product of luck--in which case, we would not consider it predictive of future success--or of some change in skill or repertoire--in which case we would be more comfortable expecting a similar performance in 2015.
Let's start by looking at the timeless sabermetric rough-and-ready indicator of luck: BABIP. Here, we see Harang was, if anything, a victim of below-average luck last year, as he suffered a .318 BABIP (.305 career average). That higher BABIP seems to be a reflection of a change in batted ball profile. In 2014, Harang became more of a groundball pitcher, dropping his FB% by 6.5% and raising his GB% by 3.4%. In general, we know that BABIP tends to be higher on grounders than on flyballs, so that probably explains the higher BABIP.
Why did his batted ball distribution change in 2014? Batted ball distributions can randomly fluctuate year-to-year as well, so we're going to have to explain that change in profile to conclude that 2015 Harang will be closer to the 2014 version than the 2008-2013 version. Other than randomness (which we want to explain away, remember), a change in a pitcher's repertoire is a frequent cause of a change in batter ball profile. It turns out, in fact, that Harang's pitch repertoire evolved over the course of 2014, as seen in the following graphs of pitch usage since 2007:
Fastball v. cutter:
Lo! and behold!, Aaron Harang has added a new pitch. That pitch is the cutter, and it was a successful pitch for him in 2014 as opponents hit .250 and slugged .321 against it; those are the numbers, basically, of a light-hitting shortstop. The cutter also produced a 46% GB-rate and a 10% linedrive rate, both substantially better than his 2014 averages of 39.4% and 22.8%, respectively.
Smartly, as is clear in the second graph, Harang slowly replaced his fastball with the cutter in 2014, which is good, since the cutter produced noticeably better results than his fastball, against which opponents hit .272 and slugged .419 in 2014. Perhaps this is what the Phillies saw in Harang that led them to, essentially, make him their 2015 version of Roberto Hernandez. If Harang sticks with the cutter in 2015, the Phillies might have found a reliable middle-to-back of the rotation pitcher and a potentially solid trade chip come July.