Running backs are smart to move on from college to the NFL after three years. The wear and tear they get from being tackled by 250 pound freight train linebackers or having to pass protect on blitzes or even stunts and twists that put a 190 pounder up against a 300 pound defensive tackle.
Their bodies take on damage that often sees RB’s move on before their time is due. Miami’s had that happen quite often over the years with Clinton Portis, Willis McGahee, Mark Walton and Deejay Dallas have all launched pro careers with eligibility remaining.