I used bad performance to define:

Not doing their job which is tickets assigned them (coding, testing, building, buying groceries etc.)

So we do have a clear definition of what needs to be done, and it's also clear that who's doing it and who's not. Only question in here might what's the accepted amount of tasks done. Like does this ticket takes an hour for X and a day for Y. In either case (Y is slacking or it takes a day for him) he's an incompetent employee and needs to go. Am I missing something?