Only two kinds of actors are bad: those who can’t be themselves and those who you wish wouldn’t be. It’s a performance of flair and precision and imparts emotion to a script that lacks it. “The Smashing Machine,” which Safdie both wrote and directed, portrays Mark (the character, as distinguished from the real-life Kerr) from the time of his first bout in the Ultimate Fighting Championship, in 1997, to 2000. The most fascinating of these traits is shown early on, when a journalist interviews Mark after his first triumph. As Mark describes his strategies, his reflections quickly outleap the specifics of the sport and take on a philosophical dimension.