It's so retarded that every team has to blame their coach for their losses when they forgot the coach isn't playing the damn ball, it's the players playing the ball though some fault could come out as a result of coach mistakes but let's be precise most teams have the fault of 30% from coach and the remaining 70%comes from the player not performing upto the task.
I think it is not wrong if every team blames the coach because the coach has a very crucial role for the performance of a team. The player selection, training method, strategy, formation, and there are many other things are decided by the coach. Even the coach has the responsibility to build the mentality of the whole players. That's why a team/club must hire a charismatic coach who can motivate the players to follow the instruction of the coach.
Anyway, I think we can determine the fault with your formula. How you can determine 30% coach and 70% players? As far as I know, a team will play based on the instruction of the coach. No player will play beyond the plan/strategy. If this happens, it means the coach has failed to manage the players even if they can win the match.
Besides, most of this team lacks discipline which is why coaches can't control players sometimes, some don't even play according to script...
If you are talking about discipline, it is also a responsibility of the coach. If there is a player who doesn't want to discipline, the coach must give the player a punishment. Even a coach can give an instruction to order a player to live with a healthy way. Even worse, if a player doesn't want to follow the instruction in the field, the coach can put him on the bench for the next match.