Oklahoma City forward Nick Collison is retiring after 15 years with the Thunder. The 37-year-old Collison announced his decision Thursday through the team. The Thunder said Collison is among five NBA players to have spent the past 15 or more seasons all with one franchise. Collison said his goal was to make a career out of basketball and that he was ”blessed to be in the NBA for 15 seasons.” Collison started 177 of his 910 career regular-season games, averaging 5.9 points and 5.2 rebounds. He and Russell Westbrook are the only two players to spend the first 10 years of the relocated franchise in Oklahoma City.