Charles Sims had a breakout season last year, producing 1,090 yards from scrimmage, split neatly between carries and catches. He was consistently productive and explosive as a change-of-pace and third-down back, and the Tampa Bay Buccaneers love him in that role.
Head coach Dirk Koetter also said that the team feels Sims can be an every-down back, if need be. That's being picked up as an indication that the Bucs may let Martin walk, but it felt more like an insurance policy statement to me: if they can't reach an agreement with Martin, Sims can at least help fill the hole, even if it's not necessary an ideal fit.