the other fear is getting made to look like a fool and getting juked out of your jock. A big guy will hit you, but as long as you wrap up and/or grab cloth, you will bring him down, however painfull it might be. I think the bigger scare is being left to tackle air as the ball carrier jukes past you on his way to a nice long run. Earl Campbell was probably one of the most punishing RBs in the modern era, but I'll but Barry Sanders kept defenders up more nights because he was much harder to bring down.
Based on that, I would say Ronney Jenkins was one of the scariest backs BYU has had. He was fast as they come, but lightning quick as well. Would have loved to see what he could have done had he been able to stay. We haven't had too many other backs like him. Heimuli had some moves, but was not at this level speed or quickness wise. Luke was blazing fast, but wasn't as shifty. Ray was shifty, but I never thought he was a true 3-down back. So there's my vote. Ronney Jenkins was one of the scariest backs to play for the Y because he had the ability to make defenders look absolutely foolish.