In an interview on The Tonight Show with Jimmy Fallon, Sylvester Stallone said that it’s a tradition for the stars of Rocky movies to be knocked out while filming, and that Lundgren delivered the hardest punch he’s ever taken.
“When you do a Rocky film, for some reason we’ve decided to have this kind of initiation that you have to get clobbered. Usually by a man infinitely stronger and larger, such as Carl Weathers… Dolph Lundgren put me in the hospital for four and a half days. It was unbelievable. He hit me so hard in the chest that the next thing I know, I was on a low-altitude flight to intensive care to St. John’s Hospital, surrounded by four nuns.”
Bonus Clip! At the end of this video is the actor playing young Creed taking his "initiation" shot!