When the A’s acquired Jake Diekman for the first time back in July, they hoped that he might pair effectively with a then-recovering A.J. Puk in neutralizing left-handed hitters, who through that point in the season had hit Oakland relievers to the tune of a .305 wOBA — not terrible, but also behind Houston, Tampa Bay, Cleveland, and New York in the American League. They also hoped that 2019 would end up being the first year since 2006 in which the A’s won a postseason series.
Neither of those things happened. Diekman, who has allowed a .293 wOBA to left-handed hitters over the course of his career, allowed a .314 figure to the 47 lefties he faced for Oakland, walking seven and hitting one with a pitch. The A’s, meanwhile, lost the AL Wild Card game to the Rays, 5-1. Diekman faced one batter.
Still, all the potential the A’s saw in Diekman last summer is still there, and so too is Billy Beane’s thirst for a World Championship. If you thought that last week’s Jurickson Profar trade was evidence of a step back from that goal (which I do not), think again. Diekman alone isn’t enough to put the A’s over the top (frankly, three Diekmans wouldn’t be enough) but teams that plan to punt on a season don’t sign relievers to two-year, $7.5 million deals, as the A’s have just done.
That said, Oakland’s decision to sign this deal with Diekman, rather than picking up his $5.75 million option for 2020 a few weeks ago, betrays a certain caution with respect to the 32-year-old. Retaining Diekman gives Bob Melvin a second lefty to pair with the recently signed T.J. McFarland (Ryan Buchter was non-tendered earlier this week), and MLB’s new rule requiring pitchers to either complete an inning or pitch to three batters means Diekman’s dead-even platoon splits will be of added value going forward (as others have noted). Then again, Diekman posted a 1.31 K/BB for the A’s last year, walking 17% of the batters he faced.
If things go right for Diekman in 2020, it’ll be because he’s found a way to pair his historically excellent and very fast fastball with better command of his slider, thereby approximating his early-career success with the Phillies and Rangers rather than his more recent adventures with the A’s and Royals. As Eric noted in his writeup in July:
Diekman is throwing harder now than he has since 2015, the year he was included in the Cole Hamels trade from Philly to Texas. His fastball is averaging 95.7 mph, which puts it among the hardest left-handed fastballs in big league bullpens, ranking fifth among lefty relievers with at least 20 innings pitched this year (only Felipe Vázquez, Aroldis Chapman, José Alvarado, and A.J. Minter throw harder). And Diekman’s stuff is especially tough on lefties because his cross-bodied, low-slot delivery creates such a unique angle on his pitches. So bizarre is Diekman’s release point that it barely fits on our scatterplot grid. He’s built to get lefties out.
During his brief stint with Oakland last summer, Diekman went to his fastball more often (58% of the time) than he had with Kansas City earlier in the season (51%) but still much less frequently than his career norm (67%). I suspect that’s largely an artifact of his tendency to go to his fastball when behind in the count, even with only one ball, which meant (given his overall wildness) that he got himself into a higher percentage of “fastball counts” while in Oakland than while in Kansas City.
Either way, I’d expect to see somewhat more of the slider next year than viewers who didn’t watch Diekman in 2019 might assume. That’s because that slider is largely responsible for Diekman’s unusually low rate of hard contact (4% “barrels,” according to Baseball Savant, compared to a league average of 7%) and his unusually high swinging strike rate (his 16.1% figure in 2019 was 10th among AL relievers). If he can find a way to keep it inside the strike zone just a little bit more often, he should have quite a lot of success. (While you don’t want a slider inside the zone too often, Diekman’s 41% 2019 mark is a little low to keep batters honest.)
The A’s could still use a front-line starter (although a crowded rotation means I doubt they’ll go after one too hard) and they’ll need to figure out who’s going to play second base during spring training, but using some of the savings from the Profar deal to shore up their most obvious weakness — their bullpen — is a hard move to argue with in principle. I’m not sure I’d have chosen Jake Diekman as the particular way to execute on that plan, but hey, Oakland knows him as well as any team can, and the club wants him back. The A’s are far from a lock to win their division next year, but that’s no reason at all not to try. And it certainly looks like they will try.
Rian Watt is a contributor to FanGraphs based in Seattle. His work has appeared at Vice, Baseball Prospectus, The Athletic, FiveThirtyEight, and some other places too. By day, he works with communities around the world to end homelessness.