expression, godan verb (-ru)
be the leader of a group of juvenile delinquents; be the boss of a gang
Colloquial expression used for the leader of a youth gang or group of delinquents. Often associated with the term 番長 (banchō).
See also: 番長 (ばんちょう)
彼は中学のとき、地元で番を張っていたらしい。
Apparently he was the boss of the local gang when he was in junior high.
It's tough being the leader of that group.