Sentence:  At the start, the underclassmen who rushed to join them emptied out of Jenkins only, but when residents in the two dorms perpendicular to Jenkins looked from their windows at what was happening in the quad, they began pouring from Neil, then from Waterford, and soon a high-spirited snowball fight was being waged by dozens of happy, hyperkinetic boys <WSD>cavorting</WSD>  in dungarees and T-shirts, in sweatsuits, in pajamas, even some in only underwear. 
Meaning of the word marked with <WSD> tags:  To move about carelessly, playfully or boisterously.