Akers might have been in the game on the first offensive snap against the Cowboys but I don't think that means much more than this: Akers was a better choice than Brown for the first play McVay wanted to run.
Henderson, as you recall, was hurt in camp and missed a couple weeks. My guess is if Hendo was 100% he would have gotten that first rep.
As the game played out Brown got 44 snaps on offense (and 18 carries for 79 yards).
Akers got 24 snaps (and 14 carries for 39 yards).
And Henderson got 5 snaps (and 3 carries for 6 yards).
To me it seems if anything Akers was getting Hendo's snaps that first game while Hendo was getting back to 100%, and in any event Brown was the primary back even though Akers got the first snap.
AlbaNY_Ram
