Sometimes, you enjoy a movie for no other reason than it's just what you need at a certain moment. Never mind why, but that's the approach I took with Ip Man 3, the third installment in a story about real-life martial artist Ip Man, the mentor who nurtured the skills of the great Bruce Lee. Much of the acting is wooden or even laughably broad, and Donnie Yen, who plays Ip Man, isn't the most expressive of performers. To its credit, though, Ip Man 3 makes little effort to disguise the fact that it's a by-the-numbers martial arts movie -- and it includes work by Mike Tyson, who rumbles into the movie like a special effect. Look, no one is going to confuse Mike Tyson with a great actor, but the former heavyweight champ adds physical menace to Ip Man 3 as Frank, a "foreign devil" who has become a boss in 1959 Hong Kong. And with all apologies to the "art" in martial arts, t a confrontation between a slugging Tyson and a supple Yen offers amusing kicks. As directed by Wilson Yip, the story turns Ip Man into a resolute protector. In one of the movie's less probable twists, Ip Man fights to preserve an elementary school that the mob wants to take over. The story eventually leads to a face-off between Ip Man and another skilled Wing Chun master, Zhang Jin. I wouldn't rank Ip Man 3 as a martial-arts leader, but choreographer Yuen Woo-ping delivers enough bracing fights to keep the movie's motor running. Lynn Hung manages to give a real performance as Ip Man's wife, but you'll have to duck to avoid the sentiment that embraces her character when Ip Man 3 tries to jerk some last minute tears. Still, with this sort of movie, you take what you can get, and there's enough here to keep all but the most demanding fans happy.