How? I've yet to see any network live up to its claim of streaming sports on the Web. In every case so far, it has been BS that requires a pay-cable subscription (thus negating the whole point). NBC is a major offender in this regard.
The one option I can think of is if you live in a city where Aereo offers service and the sports you want to watch are on network TV—namely football. I tried an antenna for that purpose but I was thwarted by a nearby hospital's medevac helicopters, which kept causing interference. I live in Philly, so I will probably give Aereo a shot, so I can see how the Eagles do. Purportedly service is coming soon.