For every successful ZBS running back in the league (namely Arian Foster, Alfred Morris) there are typically more who struggle (namely Darren McFadden, Cedric Benson, Chris Johnson, Shonn Greene) in the scheme. The list itself doesn't seem to discriminate against the players themselves and after all, some of the players who "struggled" put up similar (if not better) numbers than those who are "a success". But you must understand that whatever physical or athletic advantage a running back has, when they play in the ZBS they can only expose it after making the read; If you make the wrong read, you're not going anywhere on the play without a little bit of pure luck.
Fortunately, we've already seen what half a season of wrong reads will do to an offense, and more importantly, we've gotten a first-hand account on just how difficult it is for a players to adjust to this system. The ZBS goes against all traditional notions by asking running backs to be patient and to hit the correct (not the first) hole he sees, as well as asking him to anticipate the cutback based on what the defense will be doing, rather than specifically what is happening right now.
You can't just run downhill all the time - you have to be able to think about where your opponents and your blockers will be at the fifth step after the handoff, when you're still only about to take your second.
It's a lot to take in and handle, especially for players like Lynch, who was raised in a predominantly downhill, power blocking scheme throughout his entire career. So for him to match, and continue to outpace his early-career production, after only three to five months on the learning curve, is even more incredible.
