Madison police said a woman walking in the 400 block of State Street was knocked down by punch from a stranger early Saturday morning.
Police said someone grabbed the 20-year-old victim's arm at about 2:50 a.m. Saturday.
She turned to see who her assailant was, and was punched in the face, according to a Madison Police Department incident report.
She fell to the ground and did not get a good look at her attacker.
Police said the battery remains under investigation.