Suppose that there are two opposing armies. One army holds a fort that controls a river crossing; the other army wishes to cross the river, using the bridge that the fort guards. The defending army can either retreat across the bridge (Retreat) or remain in place (Engage). The attacking army can either attack the fort (Engage) or find another way to cross the river (Retreat). The payoffs for this game are shown below:

Attackers Engage Retreat -20 -5 Defenders Engage -20 10 10 0 Retreat -5 0