I hated that tactic in my own country, where some of my fellow rioters last year blamed covert police agents for the damage and provoking violence, and I hope you hate that tactic from your own side as well.
At least, this is my experience with large parts of the german (radical) left movement. It is allmost surreal, when you follow the left wing online news ticker about the demonstration and everything that happens. Police and fascist violence there and there and again there! And when you also follow neutral mediums or the other side, or are even there to see for yourself. Because then you can see quite some leftist/antifa violence or threats of violence, as well.
The agressors are allwas the others, the police and fascists, never they themself. And sure, police and fascists do use aggressive violence. And in numbers probably a lot more. But not only them. So it is a tactic. It is propaganda. I have seen all three sides (antifa, police and fascist) use it. And was quite some of that violence in fact done by covert police? Possible. But usually with the applause of the crowd.
(And the german right-wing movement is of course even worse at being hypocrites, because no one there is officially a rassist or a nazi and they get angry, if you point out rassist or nazi-ideologie arguments they made)