After Chris Rock delivered a G.I. Jane punchline targeted at Jada Pinkett Smith's short hair, Will Smith approached the Oscars stage and promptly slapped Rock in a shocking turn of events. Smith did a surprisingly good job of not telegraphing the technique and using his hips to generate power, but Black Belt Magazine typically doesn't approve of slapping as an effective strike (unless it is Nate Diaz's Stockton Slap). Rock demonstrated a very strong chin, taking the blow with apparently minimal damage before continuing his bit.
Many thought it may have been an act, but Smith made it evident how real it was by shouting expletives at Rock and telling him to keep his wife's name out of his mouth. Rock impressively continued the show smoothly, and Smith would go on to win the Academy Award for best actor later in the evening.