[2019] WHY? does casual has friendly fire?

Originally posted by twunny phaiv: If somebody teamkills you, they'll activate Reverse Friendly Fire, meaning any further team damage they do will be reflected back at them. This also applies for whole squads at a time.

Exactly! ^
I apologize for your negative experience. You should be reporting players abusing this behavior. You can report them by clicking their names in the scoreboard and using the in-game report button for griefing/abusive behavior.