The more I read the more I think we should all be getting excited about Ben Mason. Continue to hear that he is a prototypical "Harbaugh player and FB."
I can't read an article without some tidbit about how much a football player he is.
That said, back to the OP, I think we will continue to see multiple RBs rotate. I think everyone on this board can agree that not every back is created equal and certain situations call for a certain type of back. I think Evans is our most explosive and therefor best back (I like vision, speed, cut-ability in my RB) but Higdon and Issaac are probably not far off.
Related generic opinion: it's could depend on how good the O line is this year but IMO the left side is already solid and the center and right side are quickly falling into place. I will go on record and say that by the end of October our O line will be better than it was last year. I believe in these kids that much. It would be a no brainer for me if Newsome were 100% and playing.
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Sometimes people standing on third base think they hit a triple, but they didn't - Jim Harbaugh