Police deployed horse patrols and tactical units on South Street late Saturday to prevent a repeat of the rowdy crowds that erupted into a melee the night before.

Officers patrolled near Fifth and South Streets, where crowds had gathered until 2 a.m. Saturday. During that confrontation, police arrested Derek Langone, 25, of Chicago, for allegedly shoving and punching an officer.

Others from the crowd dispersed, police said, but Langone fought them. Police used a Taser to stop him.

None of the officers was injured. Langone was being held on preliminary charges of aggravated assault.

South Street has been hit in the past by crowds of youths who organized so-called flash mobs by using text messages and the Internet.

As of 10 p.m. Saturday, police reported the area remained quiet.

Contact staff writer Mark Fazlollah at 215-854-5831 or mfazlollah@phillynews.com.