Wiktionary
knock on the head
vb. (context transitive English) To put an end to; to defeat or frustrate (a scheme or project).
Usage examples of "knock on the head".
And he said a knock on the head like his was could lose a man his memory.
Peter, I think maybe I took a knock on the head last night and it's left me concussed.
I may not have had all my birds on the board after that knock on the head I took, but I saw what those bastards did to you and Livak.