As Smith walked the red carpet for the sci-fi premier Friday, a Ukrainian reporter tried to hug the actor, then kissed him on the cheeks before going for the lips, the news station said Saturday.
Will responded with a backhand slap to the reporter's face, saying "Come on man, what the hell is your problem buddy?"
When the two women Will was walking with turned to view the incident, the actor apologized and explained.
"The joker is lucky I didn't sucker punch him," Smith said to a nearby cameraman.
Notable deaths of 2014 [PHOTOS]
Meg Ryan, Kiernan Shipka to star in 'Fan Girl'