Who knows, the one play where Shipp hit the hole and ran over the safety, Wolfley was going nuts about what a great run it was and how tough Shipp is finishing plays. And then Pasch sort of mentioned that's the difference between Shipp and JJ, JJ probably tries to make that guy miss and break the long run, Shipp just lowered his head and ran into him. It's fun to watch, but it's also why Shipp hasn't been durable he takes so many shots.
Wolfley, a former FB, said that Shipp isn't going to get many 20+ runs but he'll put his nose in there and get what he can get, a very physical runner. He said something about we've all seen in practice that JJ can break off the longer runs we just haven't seen it in games yet.
I really get the impression that's the whole thing for Green, he thinks the threat of a 40-50 yard run is more valuable in his offense than a pounding runner like Shipp but so far with this OL it appears the opposite is true.
Start Shipp until JJ shows he's better.