This Demonstration simulates the collective behavior of chasers (red) and targets (green) in a 2D square lattice. By hopping between nearest sites, a chaser closes in on and catches its nearest target, while targets evade the nearest chaser. Giving the initial number of chasers and targets, a random configuration is created by clicking "initialize". Checking the box "run simulation" starts the game of tag. You can also change the velocity of the chasers, and the recognition ranges of chasers and targets. While the velocity of targets is fixed at 1 (individuals hop to one site in each time step), you can change the velocity of the chasers from 0 (not moving), 1 (equal to targets), and 2 (faster than targets). Each chaser closes in on its nearest target when it is within the recognition range of the chasers; otherwise each chaser follows a random walk. Each target evades the nearest chaser when it is within the recognition range of the targets; otherwise each target follows a random walk. When a target is in a nearest site of a chaser, the chaser catches the target by hopping to that site. By varying the three parameters, you can control the system from pure random-walk to chase-and-escape interactions.