Sgt. William Vojtek of the Indiana borough police department said there were numerous alcohol-related arrests Saturday and an investigation into a report of a sexual assault.
Hundreds filled the streets, causing traffic backups, as warm weather after months of frigid temperatures brought out winter-weary students and other young people.
Students said they were celebrating early because they will be on spring break on St. Patrick's Day.
Following similar disruptions last year, university officials said they had tried to head off a recurrence through educational programs about alcohol abuse and alternative weekend activities.
Officials said any students charged could face suspension or even expulsion.