expression, suru verb (irregular)
gang up on and beat someone
Colloquial expression meaning to surround and beat someone as a group. Often implies a cowardly or unfair attack.
See also: 袋叩き (ふくろだたき)
彼は帰り道で不良グループに袋にされた。
He was ganged up on and beaten by a group of delinquents on his way home.
袋にするなんて卑怯だぞ。
Ganging up on someone like that is cowardly.