Sunday punch
noun
Boxing.
the most powerful and effective punch of a boxer, especially the punch used in trying to gain a knockout.
anything, as an armed force, line of argument, etc., capable of inflicting a powerful blow on a hostile or opposing person or thing.
Origin of Sunday punch
First recorded in 1930–35
British Dictionary definitions for sunday punch
Sunday punch
noun informal, mainly US
boxing
a heavy blow intended to knock out one's opponent
any manoeuvre or action intended to crush an opponent