The Collaborative International Dictionary of English v.0.48:

Horseplay \Horse"play`\, n.
   Rude, boisterous play.
   [1913 Webster]

         Too much given to horseplay in his raillery. --Dryden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

horseplay
    n 1: rowdy or boisterous play