You can get a lot of NFL and college football from the antenna. I use my parent's cable login to cover the rest (WatchESPN) but of course that's not a real solution available to everyone.
NCAAF is a little random since some games are on non-cable but a majority aren't. I'm on the west coast and the games are usually on FS1 or Pac-12 network.
NBA is pretty much impossible until the ABC has their Sunday games and the NBA finals.