http://goallineblitz.com/game/player_awards.pl?player_id=919092He had 65 during most of his first playing season, fluctuating in the 90s his second playing season, and has dropped back to the 200s with higher levels of competition in his third playing season; Yet he's been #1 in conference O rank by the end of every season he's played.
This leads me to believe that blowout performances with extremely crappy everything else in your entire league will allot you a higher global O rank, and a more even playing field will lower your # regardless of being the best against that competition. Also of note is that my HB has progressively received less yards, touchdowns, and has a lower (though still respectable

) YPC each season. I'm sure this plays a factor but it doesn't seem to be the biggest one after watching his global O rank shift about.
Look for a level 20 HB in the D leagues who gets 30+ rushes a game and every other HB in that league being bad/under-leveled