We’ll probably look back at the 2017 playoffs with one central theme in mind: walks. I’d usually reserve this follow-up sentence for statistics that exemplify how bad Cubs relievers were, but I don’t need to because you already know that the bullpen didn’t exactly perform up to par. It was so bad, in fact, that many are pointing to the bullpen’s regression as the driving reason for Chris Bosio’s firing.

Cubs relievers’ inability to throw strikes certainly influenced the front office’s decision to say goodbye to the long-time pitching coach. In reality, though, it was more than just a two-week sample of walking batters.

We can point to Jon Lester’s confrontation with Bosio after being removed due to arm fatigue. Or we can talk about how recent acquisitions floundered with Bosio at the helm. But maybe there was another factor involved. Maybe it also had to do with the sudden decline in fastball velocity from nearly every member of the starting rotation.

Jon Lester, Jake Arrieta, Kyle Hendricks, and John Lackey all threw slower in 2017. And not just a tad slower; we’re talking almost 2 mph slower, which is a very significant drop.

2016 MPH 2017 MPH Difference Jon Lester 93.1 91.8 -1.3 Jake Arrieta 94.3 92.7 -1.6 Kyle Hendricks 88.9 86.6 -2.3 John Lackey 92.5 91.4 -1.1 AVERAGE -1.6

A reduction in velocity from Lester, Arrieta, and Lackey could be attributed to age and a heavy workload from the previous long postseason runs. Hendricks is much younger, but he too has borne a heavier burden due to the team’s success. Still, it’s odd to see the entire rotation experience an average velocity drop of 1.6 mph.

In Hendricks’ case, we noted that a lower arm slot correlated directly to lower velocity. Hendricks himself confirmed that relationship shortly thereafter, but also said that he wasn’t necessarily going for more velo. Even so, his performance down the stretch was accompanied by an uptick in the numbers on the radar gun. Maybe that’s something the Cubs insiders were aware of before Cubs Insider; it certainly should have been.

As for the others, perhaps training and conditioning methods played a role. Maybe throwing programs could have been adjusted. Arrieta has exhibited some release-point variation over the past two seasons. Could those have been tightened up? While much of this is purely hypothetical and maybe even inevitable, it all fell within Bosio’s purview.

It might not be fair to place the weight of the Cubs’ decline in velocity solely on the shoulders of a mere coach, but the brass certainly does not intend to witness a similar regression again.