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

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "horseplay":
   badness, banter, buffoonery, clownishness, discourtesy, disorder,
   disorderliness, disorderly conduct, disruption, disruptiveness,
   foolery, fooling, frowned-upon behavior, harlequinade, hooliganism,
   impropriety, misbehavior, misconduct, misdemeanor, misdoing,
   monkeyshines, naughtiness, nonsanctioned behavior, roughhouse,
   rowdiness, rowdyism, ruffianism, shenanigans, tomfoolery,
   vandalism, venial sin, vice, wrongdoing