When the pair was shooting scenes for 2002's Men In Black II, Smith wanted to show off his newfound fighting skills that he learned on boxing biopic Ali.
Despite wearing inflatable gloves as he sparred with the director, the punching prank went horribly wrong and left Sonnenfeld out cold.
Smith tells Total Film, ""We had inflatable boxing gloves so we're playing with the inflatable boxing gloves and I'd just done Ali. The gloves are huge. So we're doing this and we're playing and we're playing and we're playing, and I punched him and the glove popped and...""
Sonnenfeld adds, ""(He) knocked me unconscious.""