If Jake Diekman has pitched his last game for Arizona, his performance will put him in pretty elite company. Just not in a good way. For his 7.53 ERA ranks third all time among Diamondbacks’ pitchers with more than twenty appearances for the club, behind Eddie Oropesa (7.59 in 2002-03) and Javier Lopez, who somehow managed to make 29 appearances for Arizona in 2005, despite a 9.42 ERA. A trade-deadline acquisition from the Rangers, the D-backs inexplicably sent two players with actual pulses to Texas in exchange for Diekman: prospects Wei-Chieh Huang and Joshua Javier. It didn’t take long for Jake to make a bad first impression, walking two of the three batters faced in his Arizona debut.
Generally though, Diekman wasn’t bad through the first month. Used mostly as a LOOGY, over his first 14 appearances, he worked eight innings and had fifteen strikeouts, to go with a 3.38 ERA. That was despite a hefty .412 batting average on balls in play. Down the stretch thereafter, the BABIP remained elevated (.391), but the strikeouts dried up: he struck out only three of the final 33 batters faced. As a result, those base-runners started turning into runs. Over his final 10 games and 6.1 innings, Jake allowed nine earned runs, and walked as many as he K’d. No appeareance was more Diekman-like than the game against Colorado on Sep 21, where he threw one pitch, hit a batter, and was lifted.
Truth be told, he probably wasn’t as bad as he seemed. An overall BABIP of .400 worked against him, and with a line-drive rate well below the league average (19%, as opposed to 24%), that seems more like bad luck than allowing a ton of scorchers. Indeed, his percentage of balls in play for Arizona which were classified as hard-hit, 38.1%, was exactly the same as Clay Buchholz. No-one would mind if Buchholz came back next year. Diekman’s fielding-independent ERA (FIP) with the D-backs, while still not great at 4.77, was two and three-quarter runs lower than his ERA. And his xFIP (FIP normalized for home-run rate) was half a run better still, at 4.22.
He also dialed up ground-balls at a solid rate. His 55.0% figure was behind only Brad Ziegler and T.J. McFarland, of those with a non-trivial number of innings. Indeed, Diekman’s profile is almost like a high-strikeout version of McFarland (Diekman’s career K rate is a thoroughly solid eleven strikeouts per nine innings), a left-hander who also generates grounders (49.7% career rate, vs 43.2% MLB average). That’s the profile belonging to the kind of guy whom most bullpens could probably use, and perhaps makes it easier to understand why the team dealt for him.
Underwhelming though those 14.1 innings for the Diamondbacks certainly were, it’s likely wise for the team not to judge the pitcher on such a trivial sample size. Arizona will need a better bullpen next season: one which doesn’t implode down the stretch, and if an arm like Diekman’s can fill a slot, why not?