eh, I see this every week from multiple backs, I think they just lack either the vision or the agility to make that cut. Mark Ingram is even worse, another product of Alabama's great blocking. In his and Richardson's case, I say its agility. Ingram had a 4.62 20 yard shuttle, the same as his 40 yard dash. He has to gear down so much if he makes a cut he is getting tackled in the backfield.
Judging by the plays Richardson did fairly well on with the Browns, Id say its also agility, mostly straight up the gut plays, he just had bigger holes and a few plays where he knocked a safety over.
read the article agility trumps straight line speed. Football isn't in straight lines, what the point of a good 40 when you have to slow down so much to make a cut, and in Ingram and Richardson's case, they dont even appear to have good straight line speed.
Arian Foster ran a 4.7something but good agility and vision to find the cutback lane and had plenty of nice runs although it looks like the workload they gave him with his injuries, he is done.