Riot is a Metropolis villian who is able to duplicate himself at will and overwhelm his opponent.
The villian Roulette lured Batman into Devil's Square so that the villian team Roulette had gotten together- Roxy Rocket, Riot and Dr. Phosphorus- could take Batman out while Roulette booked bets on the outcome. It worked. However, Steph and Damian swung in to save Batman. In fact, when Riot threatened an injured Batman, saying, "I've mastered my power now, Batman! No accidental duplication from impact!" Steph quipped, "That's a shame, because we're just getting warmed up!" while she and Damian kicked two Riots in the face.
Steph led Batman away while Damian said, "I'm only maiming the real Riot if I maim the real Riot, correct?" Steph said that sounded like a plan to her. After getting Batman out of the way, she jumped back into the fray, noting that "little Lord Fauntleroy" (Damian) bit off more than he could chew." She and Damian apparently defeated Riot, because minutes later, the two heroes and Batman came to take down Roulette.
Find out more about Riot here.