A great actor doesn't just reinvent himself with each role. He thinks his way into moments that other actors would coast through on autopilot. As George ''Iceman'' Chambers, a world heavyweight champion who is stripped of his title and sent to prison on a rape charge (the implication, though never definitive, is that he's been railroaded), Ving Rhames, in Undisputed, is playing a less flaky, more self-controlled variation on Mike Tyson. But Rhames, with a shaved head, a protective scowl, and a deliberate dead-aim voice that is nearly musical in its soft threat, never allows you to pigeonhole the character. He builds him layer by layer, like a psychological brick wall, showing you Iceman's raw physical power, the fearless, even merry way he uses that power in tandem with his mind, and, finally, something more complex -- a pride in his invincibility that's his triumph and, just maybe, his downfall.
In prison, the more that Iceman tries to isolate himself, the more everyone wants a piece of him. His celebrity makes him both a demigod and a target, and so it's all but preordained that he'll have to climb into the ring with Monroe Hutchen (Wesley Snipes), a convicted murderer who was once a rising boxing star and has never yet lost a prison bout. Perhaps the best work from director Walter Hill since ''The Warriors'' (1979), ''Undisputed'' is a shrewd and splendidly volatile B movie structured around a highly original gambit of suspense. As played by Rhames and Snipes, who gains intensity by tamping down on his blade-edged cool, both of these hard cases are quite charismatic, and so the outcome of the big match isn't at all clear. Let's just say that this is one fight to the finish too lively to produce any real losers.