pile-on

n.

An activity involving several individuals jumping (or piling) on top of an unfortunate victim, forming a pile of people. This person then becomes the target of the pile-on.

Pile-ons are often deliberately instigated as pranks.

This is normally triggered by someone mentioning the words "pile on", or a word phonetically similar, e.g. "pylon".

Synonyms:

stacks-on (Australia), bundle, monkey pile, pig pile, or dog pile.