You're really going to go with that? Seriously? It's not just simple math. You do realize that rushing average is mainly compiled between the 20's, where running is a heck of a lot easier, right? That inside the 20, the field shortens and players can naturally play closer to the line? Especially inside the 5.
Wait. I just thought of something.... If a team is averaging 4 yards a carry, which is a pretty standard avg, why would they ever pass? Hell, you'll make a first down on every third carry. March it right down field and score a TD. Every. F'n. Time. It's unbelievable that no coach has ever realized this. Those stupid bastards....
Or why not give it to your RB on every 4th down when it's 4th and 3? He's averaging over 4 a carry. Guess how many times it takes him to get the first based on that average? No. Wait. There never will be a 4th and 3. I forgot about the scenario above. I'd have already got the first down on my 3rd carry. Strike that 4th down scenario. My bad.