KENOSHA, Wis. (AP) — Authorities say a 17-year-old boy was arrested in Kenosha after he allegedly stabbed a man who was attacking his sister.

The Kenosha News reports that police responded about 10:30 p.m. Sunday to a report of a person who had been stabbed.

Police spokesman Lt. Tim Schaal says officers found a 23-year-old man on the scene who told police he had been stabbed in the back by “an unknown person for unknown reasons.”

While police were interviewing the man, a woman told police that her 22-year-old daughter had been attacked by a former boyfriend and that her 17-year-old son had stabbed the man.

Schaal said teen told police he had heard his sister struggling and saw the 23-year-old man on top of her choking her.