A redditor, David Wong, was playing violin outside of a show one night, by himself, for his own amusement, and some spare change. He got a lot more: a crowd gathered round, and people started freestyling over his violin playing! The violin played along, altering his music into something that had a more obvious beat.
The first guy who stepped up gets points for trying, but he never really gets a flow going. The next guy, however, unleashes a Spanish rap that kills (in a good way) even if you can't understand it, which I couldn't. The violinist flips into a fiddle-esque riff as the freestyle gets more intense. It's fantastic, even if you don't speak Spanish. Some YouTube commenters can, however, and they chimed in: