Acting hurts.
Check out Michael B. Jordan taking a REAL punch to the face on the set of "Creed" -- and while it was totally scripted ... you can see and hear the impact.
In fact, Sylvester Stallone recently told Rotten Tomatoes that Jordan was "knocked cold" from the punch ... though he adds, "I didn't mean for that to happen."
Either way, Jordan says this shot was the exact moment he was "initiated into the world of Rocky" -- and he's pretty proud of it.
Article courtesy of TMZ