Raiders have an action with downed Survivors called Finish Off. It's a short timed interaction that provides the Raider with Energy, so they will be doing it all the time. Interrupt this.
This can be annoying as more recent and popular Raiders such as Ginyu, Broly, and Black have extremely short interaction times for Finish Off. I suggest tailing a Freeza or Cell player from out of sight and interrupting them when they go to finish off someone.