What does Judges 20:31 mean?

When the Benjaminites came out to fight, they were drawn away from the city. They started killing Israelites, just like before—about thirty men fell in the open fields and on the roads leading to Bethel and Gibeah. Judges 20:31 - Modern Text Bible

(Benjamin thinks they’re winning again, as they kill some Israelites and chase them away from the city.)