Highway Robbery is the name given to an unmarked secondary quest in The Witcher 3: Wild Hunt. Four level 3 peasants are begging for help. As you approach, however, they turn aggressive and you must kill them. This can occur within Velen. The peasants are all male and typically carry maces with minimal armour.
Take a stroll through the forested pathway that winds from the Boatmakers' Hut to the Northwest of the Hut, towards Crow's Perch, and you may uncover a trader being attacked by three bandits. As you arrive, the trader turns out to be a bandit too—a ploy to trick any would-be heroes! Quickly slay each of them, and any nearby wolves.