Money is generally considered one of the great motivators. Even though players in the NFL have a lot of money, it's still true for them. The reality is that the NFL is a business, and players are always playing for their next contract.
I put an asterisk beside Roquan Smith's name because I fully expect him to receive a contract extension prior to the season and not play in the last year of his deal. I think this would be a very smart move by GM Ryan Poles. When you have a player of Smith's caliber, you do not let him test free agency...