Recently, a new concept is proposed for chasing and evading in crowds, called "group chase and escape" through a simple model. In this model, two kinds of players, chasers and escapees, play tag on a two-dimensional square lattice. Each chaser approaches its nearest escapee. On the other hand, each escapee steps away from its nearest chaser. Although there are no communications within each group, players appear to cooperate among themselves to chase or escape. We found relation between this cooperative behavior and group formations depend on the density of chasers and targets.