Consider a toy model of interaction between the MBTA Transit Police and riders. There is a fine f > 0 for being caught free-riding, so riders prefer to pay $3 for the ride if they are checked. Otherwise, they prefer to free-ride and keep the $3. Checking is costly, so the Transit Police incur a cost of $1 if they check, irrespective of whether the rider has paid the fare or is free-riding. However, when they do catch a free-rider, the moral satisfaction offsets the cost of checking, so they get the payoff of $3+f in this case. The game can be represented in the following normal form