A rap battle is a showdown of lyrical skill. It's where competitors grab the mic and lay their thing down. To win, you must humilate and bring down your opponent.
The best example of freestyling in movies is the film 8 Mile, in which Eminem makes everyone around him look like a stupid asshole.
Then there's this guy.
All these movies seem to glorify what rap battling actually is. Very rarely do gangs get involved, given as they're busy with crime and all. The reality of this scene is less hardcore than most people think, and the rappers themselves are too.
...there are way too many people doing this. The above photo shows the actual nature of most freestylers. Whether it's alcohol or ego fueling this scenario, I don't want to be there.
These guys are gangster.