The NFL is close to adopting a policy that would prohibit a player from re-entering a game that he exits with a concussion-related injury. The policy will go into effect once the league and the NFLPA sign off on the document. "We're really at a stage where we're dotting the i's and crossing the t's," Dr. Thom Mayer, the NFLPA's medical director, said on Saturday. "We're waiting on the final draft."