On the same day the Red Wings announced they signed college free agent defenseman Robbie Russo to a 2 year entry level contract, the team also elected not to sign Ben Marshall to a contract; Marshall is now a free agent.
When the Wings drafted Marshall in 2010 with their 7th round pick(201st overall), they thought he had the potential to become a dynamic offensive defenseman who could quaterback the power play. His great wheels, dynamic offense, puck rushing, first pass, hard shot, and offense first mentality led the Wings to draft him, but there's also good reason why it was in the 7th round and not sooner. One scout early on said Marshall might make an interesting forward project if defense didn't work out. On the flip side, he needed to work on his defensive game to show he wouldn't be a defensive liability and needed to use better judgment with his offensive pinches.
In 4 seasons with the Minnesota Golden Gophers, Marshall averaged 0.38 points per game, ranging anywhere from 2nd to 4th highest scoring D man on the team. The Wings took little risk on a player they hoped could provide big rewards, and those rewards never came to fruition. Some of that is because Marshall didn't develop enough defensively to be a 2-way D man in the Wings system, but it's also due largely to the better prospects the Wings have drafted in the meantime. Marshall wasn't going to make the Wings team, not with the depth they have knocking at the door already, and I believe his defensive game never developed to the level that the Wings would have required for making the big club. Marshall wasn't going to make the Wings team, and Grand Rapids is already bursting at the seams with better defensive prospects.
I look at it this way, Marshall wasn't good enough to make the Red Wings, and the team picked up a free agent college defenseman in Robbie Russo who's a much better, more skilled prospect and who has a better chance of making an impact on the team and organization. Why sign Marshall to a contract when you've already determined there's not a place for him. They essentially upgraded defensive prospects by letting Marshall become a free agent and picking up a better one on the same day.