Anyway, here's the opinion in Northwestern University and College Athletes Players Association. The decision notably holds that Brown University is inapplicable, but goes on to analyze the factors under Brown anyway (reaching the same conclusion - football players are employees). In Brown, the NLRB held that graduate student assistants were not employees.
I know everybody is excited/infuriated/elated about this decision, but a quick reality check: this will be appealed. The NLRB will review it and it will probably end up in the federal courts. I would be surprised if Northwestern football ever unionizes as a result of this petition. That said, agencies and courts have surprised me before.
One other quick note, many college football teams play for public colleges and universities. Those schools generally fall under a state public employee relations act (PERA). So, this decision will not directly affect them (it may provide some "persuasive" authority to the state labor relations boards though).
Image: NLRB seal used in commentary on NLRB. Not official use.