It may be that it's to "protect" the commercial interests of the sporting organizations, but the no drone rules do exist.
Quoted from the FAA site (my link above) - emphasis is mine:
PURSUANT TO 14 CFR SECTION 99.7, SPECIAL SECURITY INSTRUCTIONS, COMMENCING ONE HOUR BEFORE THE SCHEDULED TIME OF THE EVENT UNTIL ONE HOUR AFTER THE END OF THE EVENT. ALL AIRCRAFT OPERATIONS; INCLUDING PARACHUTE JUMPING, UNMANNED AIRCRAFT AND REMOTE CONTROLLED AIRCRAFT, ARE PROHIBITED WITHIN A 1410271420-PERM END PART 1 OF 3 FDC 4/3621 FDC PART 2 OF 3 SPECIAL 3NMR UP TO AND INCLUDING 3000FT AGL OF ANY STADIUM HAVING A SEATING CAPACITY OF 30,000 OR MORE PEOPLE WHERE EITHER A REGULAR OR POST SEASON MAJOR LEAGUE BASEBALL, NATIONAL FOOTBALL LEAGUE, OR NCAA DIVISION ONE FOOTBALL GAME IS OCCURRING. THIS NOTAM ALSO APPLIES TO NASCAR SPRINT CUP, INDY CAR, AND CHAMP SERIES RACES EXCLUDING QUALIFYING AND PRE-RACE EVENTS. FLIGHTS CONDUCTED FOR OPERATIONAL PURPOSES OF ANY EVENT, STADIUM OR VENUE AND BROADCAST COVERAGE FOR THE BROADCAST RIGHTS HOLDER ARE AUTHORIZED WITH AN APPROVED AIRSPACE WAIVER.
If I am reading this correctly, remote controlled aircraft are prohibited from being flown 3 Nautical Miles (a little less than 3-1/2 miles) of any major league baseball or football and NCAA Division 1 (the bigger schools?) stadium with a seating capacity of 30,000 from an hour before a game, up to an hour after the game.
I guess open-air hockey, soccer, smaller schools and minor leagues are OK (at least in the US). I could see where you could get into some trespassing issues, depending on the location, but that's not the same thing as a NFZ.
As far as tomorrow's game, it looks like the NFZ is 32 miles.
New FAA video explains that the Super Bowl is a No Drone Zone