It's called an Antenna....
Increasingly, no. Many sports are switching to subscription channels (ESPN, Fox Sports, Root Sports, CNBC/MSNBC, etc.) with limited or no legal options for streaming. MLB is there today and has a decent product; Olympics are ok; NFL is pretty much absent. I'm not sure about the NBA or NHL.
Most of the channels I can receive over the air (networks) don't carry much of interest to anyone in my household. But we watched so little TV that we went ahead and got rid of cable anyway. I did subscribe to MLB.tv, though (and am much happier than what we had from basic cable since I can now watch the teams of interest to me).
I suspect cable companies will be in trouble should the NFL decide to start streaming their games. I doubt this will happen, though; they're getting a ton of money from ESPN to stay right where they are (and most folks are resigned to just keep paying for cable to watch NFL games).