Last week, right before halftime, I was watching the scoreboard scroll at the bottom of the game :

6-0
3-10
6-6
3-6
et cetera

SUMMATION:
I believe it was Cowher that said it takes the offense 4 regular season games to get up to speed; whereas, defenders simply have to "run into people" and "create havoc" (so, they are able to look better earlier).