Paul Aufiero is best described as a man-child. At 35, he lives with his mom, thinks that 10:46 p.m. is a little late to be heading out to a party, and sleeps with a poster of his idol, fictional New York Giants star Quantrell Bishop, above his bed. In writer-director Robert Siegel’s new movie “Big Fan,” Paul becomes the unlikely subject of an engaging and darkly humorous character study. Building on his work with 2008’s critically acclaimed “The Wrestler,” Siegel puts a new spin on the culture of athletic obsession, glimpsing into the life of a pathetic fan on the cusp of middle age.

Paul (Patton Oswalt) lives for the New York Giants, calling into radio shows with pre-scripted diatribes about how his team will make it to the Super Bowl this year. When he’s not working as a parking attendant, he sits outside the football stadium, watching games on a small TV rather than sitting in the bleachers. His ongoing call-in war with mysterious Eagles fan “Philadelphia Phil” (Michael Rapaport) probably gives him the greatest sense of purpose his humble life has ever known.

Oswalt—whose previous credits include voicing Remy the Rat in “Ratatouille”—gives an evocative and authentic performance. His naturally chubby physique complements his character’s infantile personality, both of which serve to present a man at odds with the world around him. Paul’s obsession extends beyond the realm of football; he’s created a lifestyle of blithe immobility and self-neglect on which he refuses to loosen his grip. Even his most immature moments—yelling at his mother for interrupting his 15 seconds of radio fame, scarfing down Chinese food and Mountain Dew until his head aches—act as part of a system Paul has developed for himself to resist his increasingly evident lack of a career or family.

On a boring night out with friend and fellow Giants fanatic Sal (Kevin Corrigan), Paul happens to run into Quantrell Bishop at a nightclub. The conversation takes a turn for the worse and Paul ends up brutally beaten by Bishop and hospitalized for a number of days. Paul’s family wants to see him enact the revenge he deserves in court, but Paul just want to see Bishop off the ineligible list and back on the gridiron. Being assaulted by an idol may be far-fetched, but the surreal conflict presents the familiar challenge of balancing one’s personal loyalties.

The rest of the characters serve primarily as sources of advice and criticism for Paul. His brother is an ambulance-chasing lawyer with a vapid trophy wife, his friend Sal only encourages his rabid fandom, and his mother has long since given up attempting to make him to do anything with his life. While these characters are realistic archetypes, each one performs a single function and never deviates from that purpose. (As Philadelphia Phil, Rapaport spends almost all of his scant eight minutes of screen time chanting and jeering in a sports bar).

Though the plot leaves a few loose ends, these work within the film’s internal logic. The Quantrell Bishop storyline is abandoned in order to focus on Paul’s meeting with Philadelphia Phil, but in the scope of the film, this makes sense. Paul never follows through on his commitments or interactions. He is content to simply let things go, so long as he can resume cheering for the team he loves.

Siegel, formerly a writer for The Onion, has a knack for crafting characters that aren’t exactly living the dream. This was evident in “The Wrestler” and is echoed here. But rather than portray a man who has fallen from former glory, his directorial debut brings to life a character that has never and will never achieve glory, or any semblance of an independent life above mediocrity. This choice makes “Big Fan” perhaps a more pessimistic movie, but one with a perspective just as thoughtful.