(Some children are playing a game of Capture the Flag.)
Billy: Oh no! Sarah has a water gun!
Erica: We’ll have to fight fire with fire. Get the hose!

Fighting fire with fire means using the same weapon or technique that your enemy is using. In the example above, fire represents water. You actually can fight fire with fire. In order to stop the spread of a wildfire, firefighters sometimes burn all the plants on a strip of land in the fire’s path. When the fire reaches the bare ground, it has nothing to burn and cannot cross over to the other side.