it's how good is their offensive line at run blocking, how good are their running backs (and you can include Mitch in this, as I'd imagine there'll be some designed run options for him in the offense). it can't just be based on stats (especially traditional ones) because of how much context matters. football, both in the inherent small sample sizes and in the more complex nature of the game, does not lend itself to that type of objective statistical analysis, and most elements have to be evaluated subjectively.