We'll be going through every position group to see if the Tampa Bay Buccaneers improved there, compared to last year. Let's start with an easy one: running back.
2015: Doug Martin, Charles Sims, Bobby Rainey, Mike James
2016: Doug Martin, Charles Sims, Mike James, Storm Johnson, Peyton Barber, Russell Hansbrough
A quick glance says the Bucs got worse at this position. They lost Bobby Rainey, and got a few undrafted backs and Storm Johnson in return. I'm not counting the fullbacks -- they have more of a tight end role anyway) -- so that doesn't really leave much room for improvement.
There is one argument to be made, though: this group didn't look all that great in the run-up to the 2015 season. Doug Martin was coming off two terrible seasons, and the Bucs declined to pick up his fifth-year option. Charles Sims had been disappointing and injured in his rookie seasons. Bobby Rainey was okay, but Mike James had done nothing the previous season, in part due to injury. It wasn't hard to believe that the running back position was going to be a real problem last year.
Of course, the opposite happened. The Bucs had arguably the strongest running game group in the NFL last year, they certainly had the most productive one in terms of raw numbers, and Doug Martin earned a shiny new contract. Whether the Bucs are better or worse this year will depend mostly on whether or not Martin can live up to his new big deal. That's far from a shoe-in, given that he's only done so in two out of his four seasons in the NFL so far. If Charles Sims can continue to get a little better and one of the team's undrafted backs turns into a quality player, the Bucs might actually be slightly better off.
Those are a lot of ifs, though. More likely, something will go wrong. Injuries will happen, players will decline, undrafted free agents will turn out to have been undrafted for a good reason. That doesn't mean the running game is likely to collapse, but it'll be difficult to get to the same level as last year.