come out swinging

verb

a) To initiate an encounter or interaction by behaving in an unrestrainedly aggressive, confrontational, or accusatory manner.

New York baseball commissioner Bowie Kuhn, rolling up his sleeves and coming out swinging for the first time Monday, bluntly told Pete Rozelle to quit "kidding the people" about football being the nations no. 1 sport.

b) To display spunk and strength of character, especially when rising above or when fighting back against trouble or adversity.

So ingrained is the instinct for massive retaliation that Downing St. came out swinging before mastering the facts.