Dwayne "The Rock" Johnson's dedication to his role in The Smashing Machine was steadfast - so much so, the actor almost got knocked out cold on set. Johnson, 53, revealed that one scene in the biographical sports film, in which he portrays MMA fighter Mark Kerr, left him weak in the knees after he was punched incredibly hard. "It felt like when you get rocked by a real fighter multiple times," Johnson told CBS Sports during a combat sports media roundtable for the upcoming Benny Safdie-directed movie on Monday, September 22.