To produce or perform (something) admirably or forcefully.
To fight, incite to fight, or approach with the intent to fight; to make a stand.
(by extension) to accomplish or produce something in a grand, respectable, or successful manner; to "represent".
To make an individual contribution to a group effort (e.g. money pool, collaborative record album)
"We're goin' in on a pizza; you in?" "Yeah, I'll throw down."
To drink a large amount of beer quickly.
"We need to finish these five pitchers in half an hour, so throw down as fast as you can!"