Beginning with the paranoid, conspiracy-mongering brother on the alien-attack series “Invasion” and continuing with the slacker best friend of the soul-hunting hero on “Reaper,” Tyler Labine has made a specialty of playing lovable misfits who rise to the occasion.

You might wonder then whether it was a good idea to take on the same kind of part in “Sons of Tucson,” a new sitcom beginning Sunday night on Fox. One answer is that this was Mr. Labine’s chance to headline a prime-time series on a major network, so typecasting be damned. Another answer is: No. It wasn’t a good idea.

As Ron Snuffkin, a good-natured loser and congenital liar who’s hired by three boys to pose as their father, Mr. Labine should be on familiar ground. Ron’s job at a big-box sporting-goods store is oddly similar to the one Mr. Labine’s Sock had at the home-repair store in “Reaper.” But “Sons of Tucson” forces Mr. Labine to do something he hasn’t had to do before on television: play the straight man.

The three brothers, played by Matthew Levy, Frank Dolce and Benjamin Stockham, have stolen his accustomed role. They’re the loose cannons, given the best lines and allowed to swear and punch and break things; they’re written, in descending order of age, as a metrosexual smoothie, an uptight 1950s dad and a budding sociopath. The talented Mr. Labine is left to play the same pratfalling sitcom father we’ve seen a thousand times before, albeit one who forgets what his last name is supposed to be and has to sleep in the tool shed behind his not-sons’ suburban manse.

That’s not a good sign for the show, which doesn’t have all that much going for it beyond Mr. Labine’s presence, however muffled. Sunday’s premiere sets up the post-Madoff premise: the Gunderson boys (who are presumably several years younger than the 9-to-16-year-old actors who play them) have left New Jersey, where their father is in jail for fraud, and traveled by themselves to Arizona, where he owns a house. Needing an adult to enroll them in school, they offer Ron $200 to put on one of their dad’s suits and play the part for an hour.

He sticks around after the hour’s up, of course, striking a deal to continue the charade while moving into that tool shed (he’s been living in his car) and trying to talk his way into a room in the main house. The humor comes from the brinkmanship between Ron and his precocious charges; he may be a con artist, but he can’t out-con a television child. Unfortunately this is the type of show in which he can, after taking his lumps, bond with that child by teaching him how to throw a baseball.

That kind of sentimentality separates “Sons of Tucson” from an obvious forerunner, “Malcolm in the Middle,” in which the adult characters played by Jane Kaczmarek and Bryan Cranston were more whacked out than their sons. The shows share some DNA: Todd Holland, who directed the “Tucson” pilot, was a producer and director of “Malcolm,” and like “Malcolm,” “Tucson” is making its debut as the odd show out in Fox’s Sunday-night animation lineup.

The way the show blunts Mr. Labine’s edge is of a piece with the way it tries, uneasily, to navigate a course between standard family sitcom and postreality metacomedy — a task already easily handled this season by “The Middle” and “Modern Family” on ABC. That tension even infiltrates the language. Confronted with a sleeping Ron, one of the boys calls him a “lose wad.” It’s as unnatural — and just about as funny — as everything else about the show.

Created by Greg Bratman and Tommy Dewey; directed by Todd Holland; Justin Berfield, Matthew Carlson, Jason Felts, Mr. Holland and Harvey Myman, executive producers. Produced by 20th Century Fox Television and J2TV.

WITH: Tyler Labine (Ron Snuffkin), Frank Dolce (Gary Gunderson), Matthew Levy (Brandon Gunderson) and Benjamin Stockham (Robby Gunderson).