Complex sentence: Owens asked Vince not to promise that he wouldn't be fired or suspended for attacking a McMahon agreed but when they shook hands, Owens headbutted McMahon and split his head open.
Split into simpler sentences: Owens asked Vince not to promise that he wouldn't be fired or suspended for attacking a McMahon. Vince agreed but when they shook hands, Owens headbutted McMahon and split his head open.