Robert Siegel, who wrote “The Wrestler,” also directs his new script, another gritty character study set on the fringes of the sports world. This time, however, the milieu isn’t grappling but pro football—not, though, the rarified atmosphere of the pigskin superstars but that of the pathetic fans who literally build their lives around their heroes. Like “The Wrestler,” “Big Fan” is actually reminiscent of kitchen-sink dramas of the 1950s about lower-class people leading lives of quiet desperation and going nowhere in the process.

But it may even more difficult to identify with its subject, chubby, nondescript Paul Aufiero (Patton Oswalt), a Staten Island schlub in a dead-end job whose sole joy is cheering on the New York Giants and calling in to a local sportstalk show to do verbal battle with Philadelphia Phil, a loudmouth fan of their hated rivals, spouting rants that he laboriously writes beforehand while working as a cashier in a parking garage. Paul, who lives at home with his nagging mother (Marcia Jean Kurtz), goes to the home games with his even scruffier buddy Sal (Kevin Corrigan), who idolizes him for his radio appearances. But the two can’t afford actual tickets; they sit out in the parking lot, watching the game on a black-and-white TV and screaming as though they were in the stands.

One night the two glimpse their idol, linebacker Quantrell Bishop (Jonathan Hamm) on the street, and follow him and his crew to a Manhattan strip club, where they use their limited resources, both monetary and intellectual, to figure out a way to approach the star. Unhappily, their inept efforts result in Bishop’s attacking Aufiero, who winds up in the hospital seriously injured.

The dramatic issue on which the rest of the picture depends is simply whether Paul will be able to overcome his addiction to football in general and the Giants in particular to see to it that Bishop is convicted of assault. It already preys on him that Bishop’s been suspended pending the resolution of the case. So when he’s approached by a police detective (Matt Servitto) to give evidence, he puts the guy off, and when his brother Jeff (Gino Cafarelli), a seedy lawyer, suggests a lawsuit against Bishop, he reacts in a fury. Matters aren’t helped by his mother’s constant harping over his late-night sportstalk phone calls and her insistence that he find himself a girl and take a job with his brother-in-law at a buyer’s club.

The pressure ultimately takes a creepy turn when Paul decides to go to Philadelphia and find his nemesis Phil (Michael Rapaport), who turns out to be as fanatical as he is. But while he builds considerable tension, Siegel upends expectations to close the picture not with a bang but a whimper.

The result is a peculiar but oddly effective portrait of a seemingly ordinary little man who devotes himself so single-mindedly to his obsession that he shuts himself off from any other possibilities in life—a fact symbolized in his job, which keeps him enclosed in his little cashier’s stall, cut off from real human contact, for most of the day. Oswalt is dead-on as the sadly realistic protagonist, as are the supporting cast, from whom Siegel draws performances that are colorfully reflective of the NYC milieu without becoming simply cartoonish. (It’s always fun to watch Corrigan do his slacker routine, so good that you wonder whether it’s acting or just himself.) And Rapaport is so perfectly obnoxious that you can understand Paul’s hatred of him, even as you pity Paul for not seeing that they’re two sides of the same coin.

No one will accuse “Big Fan” of prettifying the story—Michael Simmonds’ camerawork is deliberately grungy, accurately capturing the seedy locations—including the parking lot of the Meadowlands on game day. But the dreariness exactly suits the piece.

This isn’t a tale that’s going to lift your spirits, nor does it offer the hint of redemption that “The Wrestler” did, even as it worked its way to an ending that was tragic in an Arthur Miller, Rod Serling sort of way. Instead it’s content to be as plain as the fellow it’s about, and, despite its shafts of grim humor, in the final analysis as depressing—an unflinching portrait of a loser not so much trapped as unwilling to try to escape.