I've been fixated on our running game lately. While trying to find a website that lists the team's average yards per carry by season, I stumbled on this site:
It didn't have exactly what I was looking for, but a quick scan of the rushing leaders showed Ty Isaac at 5.9 ypc. He's somewhat down the list, but that's because it apparently includes everyone, including Joe O'Donnell who gained 50 yards on 1 carry in 1963. (I don't know, maybe after that stellar first carry, you give him the ball again?)
So I took the data and filtered it by number of carries. I chose 100 as a nice round number. That should limit the list to primary ball carriers or multi-year backups. If you argue that number is too low, there have only been 88 players to crack that. The top 10 running backs, since 1956, in terms of yards per carry (min 100 carries) are:
Isaac's average is boosted a little by one long TD run he had in 2015, but he also averaged 5.9 YPC in his one season at USC. Here's hoping he figures out whatever it is that's holding him back (pass blocking, fumbles? other?) and he gets more productive playing time next season.