Wayne Gretzky ain't exactly up in arms about the punch Brad Marchand threw at the back of an opposing player's head Tuesday night ... telling TMZ Sports, "We've all been punched."
Marchand's been under fire -- some people calling the Bruins star a cheap shot artist -- after socking Columbus Blue Jackets defenseman Scott Harrington in the 3rd period of Game 3.
Harrington was on his knees outside the crease when Marchand took a shot at the defenseless player -- before skating away before the refs could see what happened.