Sunday punch

noun
1.
Boxing. the most powerful and effective punch of a boxer, especially the punch used in trying to gain a knockout.
2.
anything, as an armed force, line of argument, etc., capable of inflicting a powerful blow on a hostile or opposing person or thing.
Origin
1930-35
British Dictionary definitions for Sunday punch

Sunday punch

noun (informal, mainly US)
1.
(boxing) a heavy blow intended to knock out one's opponent
2.
any manoeuvre or action intended to crush an opponent
Slang definitions & phrases for Sunday punch

Sunday punch

modifier

: rockets, the ''Sunday punch'' weapon of the war

noun phrase
  1. A very hard and effective blow or assault, with the fist or otherwise: and lay his Sunday punch on your snoot (1929+ Prizefighting)
  2. strong and effective pitch, esp an overpowering fastball (1952+ Baseball)