Speed is really the only thing that matters =/ SC Off-Tackle doesn't always get you a big run.. GL Off-Tackle works a lot better for me. Everything is random so when a DT engages, he will either stay engaged with the OL, swim move to the right, or swim move to the left. I've had 10 yd rushes with LaMont Jordan before using GL Off-Tackle.. LaMont Jordan is terribly slow..
You either are not running it right, have bad luck, or need a better/faster RB. The faster the RB, the faster he's away from the DL swim moving in..
Go check our franchise; I have no idea what the run ratings are for my OL but I rushed for 100 yds my last game vs the CPU.. I just used GL Off-Tackle the whole time.. I also rushed for 100 yds with Vince Young, but I ran out of the pocket everytime so I wasn't near my OL.
I also went up against a guy that used the 4-4 D.. I was getting great runs with DeAngelo Williams then too. I had a 60 yd rush for a TD.. My OL is terrible. If they aren't.. then somehow organizing your team by height means that you'll have a high run footwork/strength.
Remember:
LT: 6'9"
LG: 6'7"
C: 6'5"
RG: 6'3"
RT: 6'1"