Billy "The Great" Hope, the light-heavyweight champ played by Jake Gyllenhaal in the shamelessly melodramatic, shamefully entertaining Southpaw, is the kind of fighter famous for being able to withstand impossible pummeling, round after round after round. Somehow, Billy always bounces back, bloodied and bruised and knocking his opponents to the mat after they've exhausted themselves. His record is 43 and 0.

The fight that opens Antoine Fuqua's pounding pugilist saga, Hope vs. Jones at Madison Square Garden, is no different. Billy's wife, Maureen (Rachel McAdams), and Billy's manager, Jordan Mains (Curtis "50 Cent" Jackson), watch from ringside as their boxer gets beaten to a pulp. Their worried looks say maybe this is the one - the one that's going to take Billy down.

But Gyllenhaal's up-from-the-street fighter, all pecs and abs and tats ("Fear No Man," in old Gothic font, rides the back of his broad shoulders), wins the match, takes the title.

Only then does everything come crashing down.

If boxing movies offer a metaphor for life - tales of struggle, punishment, endurance, transformation, and redemption - this one, written by Sons of Anarchy's Kurt Sutter, is a glutton's smorgasbord of life lessons. I'd like to say that the filmmakers never met a 'phor they didn't like, but puns are cheap.

Originally conceived as a vehicle for Marshall Mathers, a.k.a. Eminem - a follow-up to the rapper's 8 Mile - the film wasn't originally set in the boxing world at all. But its hero got banged around anyway, watching a close friend die and having to fight to keep custody of his kid.

In the new, improved version, Billy watches the very closest of his close friends die, and then, wracked by grief and rage, he watches as everything is taken from him: his title, his mansion, his Maserati, and the custody of Leila, his little girl (Oona Laurence). His manager soon abandons him, too, as does most of his posse - friends he grew up with in the orphanage in Hell's Kitchen.

Good thing the soft-spoken trainer Tick (gentle giant Forest Whitaker) is willing to give Billy a job at the neighborhood gym. And good thing Tick says Zen masterly things such as "boxing is like a chess game." And good thing somebody knows somebody at the boxing commission who might be willing to cut Billy's suspension short so he can fight the big comeback fight at Caesar's Palace. (Another life lesson: If you're a professional boxer, don't head-butt the referee.)

What keeps this cornball business from getting out of hand is the commitment of Gyllenhaal, whose performance is fierce and muscular, in and out of the ring. And when he is in the ring, the boxing sequences are shot and edited with aplomb (by HBO Boxing cameramen). Not the slo-mo artistry of Raging Bull, but a wheeling, you-are-there intensity. Blood, sweat, fears.

Laurence, one of the original quartet of stars in Broadway's Matilda, is a kid actor whose lack of self-consciousness puts the grown-ups around her in stark relief. When a judge assigns Leila to the care of Family Services, the cries of anguish in the courtroom - Billy pleading to the judge, Leila pleading to her dad - resonate with despair. Southpaw should not be seen as a primer for good parenting - Billy's anger-management issues, his recklessness with weaponry and booze, result in all sorts of trauma for his kid.

But don't give up hope. And don't give up on Billy Hope. You'd be foolish to do so.