I don’t think either would be a mistake because the Bucs have needs at both positions. But there’s a longstanding rule of thumb in the NFL that you don’t take a running back early in the draft.
If you think that theory is outdated, you may want to take a look at this Insider post from Football Outsiders. It lays out some pretty convincing evidence that there’s not a lot to be gained by drafting a running back early in the first round.
The five leading rushers over the last five seasons are Adrian Peterson, Maurice Jones-Drew, Steven Jackson, Chris Johnson and Michael Turner. Those five have combined for two playoff wins as starting running backs (and that doesn’t include two playoff victories Turner had as a backup to LaDainian Tomlinson with the 2007 Chargers).
The column then points to the backfields of the two Super Bowl teams. The New York Giants had Ahmad Bradshaw (a seventh-round pick) and Brandon Jacobs (a fourth-round pick). The New England Patriots had a pair of undrafted running backs in BenJarvus Green-Ellis and Danny Woodhead as well as third-round pick Stevan Ridley.
Yes, the Bucs need someone to pair in the backfield with LeGarrette Blount. But, unless they believe Richardson is the kind of player who can be an exception to a rule, they might be wise to wait until later in the draft -- or use free agency -- to add a running back.