WordNet (r) 3.0 (2006):

set upon
    v 1: assail or attack on all sides: "The zebra was beset by
         leopards" [syn: beset, set upon]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "set upon":
   ambush, assail, assault, attack, blitz, bushwhack, come at,
   come down on, crack down on, descend on, descend upon, fall on,
   fall upon, gang up on, go at, go for, harry, have at, hit,
   hit like lightning, jump, land on, lay at, lay hands on, lay into,
   light into, mug, pitch into, pounce upon, pound, sail into, set on,
   strike, surprise, swoop down on, take the offensive, wade into