That’s what I’m trying to figure out. I agree that on certain route types, the QB can markedly increase YAC by throwing an accurate, well-timed pass. The slant and shallow cross are the routes where YAC is likely most affected by QB accuracy. The problem is, there is a lot of noise in YAC, because the majority of its causes are outside the quarterback’s control. Even over a full season, a handful of fluky long YAC plays can really distort a QB’s numbers. Remember Victor Cruz turning a 10 yard pass into a 99 yard TD with one broken tackle? Those types of plays make a huge difference in the short run, but largely even out over the course of a career.

Subjectively, there are some instances where we can be pretty sure that YAC is a product of the quarterback’s skill. Steve Young is a great example, because he played in a West Coast Offense where timing and accuracy are paramount. Year after year, he was among the league leaders in both Comp % and Y/A, which signals to me that he was a major contributor in generating YAC for the 49ers offense.