Witnesses told police two men who had just met on the street got into an argument over lyrics while in the midst of free-style rap battle early Sunday morning.
Police the argument led to a fight between six people, each rapper and two of their friends.
One vocalist, who was visiting Madison from New Jersey, was punched in the face and knocked out, police said.
He was treated at an area hospital, police said.
The man who faces possible battery charges is described as a white man, about 6 feet tall with a slender build. He was wearing a white jersey-type shirt with blue, red and white stripes and a hat, police said.
Anyone with information about the incident is asked to call Madison Area Crime Stoppers at 608-266-6014.