Can a pasty guy in tiny underpants save a movie? Simon Pegg, the English writer and actor behind the larkish spoof comedies "Shaun of the Dead" and "Hot Fuzz," has such an inherently trustworthy face that it's easy to buy every ridiculous little thing he does. In "Run Fatboy Run," David Schwimmer's directorial debut, Pegg plays Dennis, an underachieving Londoner who, as the film opens, is about to marry his pregnant and incredibly lovely girlfriend, Libby (Thandie Newton). For reasons that aren't explained until later (and which are barely believable even then, although once again Pegg's expressive, honest eyes sell us on this figurative swampland of a plot), he skips out on her at the last minute. Five years later, he's trying to win her away from her rich, athletic American beau, Whit (Hank Azaria), and he thinks entering a marathon is the way to do it. His first training costume consists of a David Bowie T-shirt, black socks worn with strange, dark sneakers, and a pair of miniature blue-and-white shorts that make his legs look like two logs of clumsily homemade pasta.
The sight of Pegg in those very small smalls is one of the best visuals in "Run Fatboy Run," and it's not the only time he seems to be carrying the picture on his sturdy, if not brawny, shoulders. If you can get past its toothpick of a premise, "Run Fatboy Run" is a perfectly enjoyable light comedy. It's also just good enough that I wanted it be better. Schwimmer, to his credit, doesn't clamp down on the material. (The script is by Pegg and Michael Ian Black, who was a member of the comedy ensemble the State and a regular on "Reno 911!") He knows enough about comedy to understand that you have to let it breathe, and as a result he may not give individual scenes enough shape and structure. Still, Pegg and his fellow actors (particularly the Irish writer and comedian Dylan Moran, who plays Dennis' dissolute best friend, and Harish Patel, as Dennis' robust, perpetually annoyed landlord) manage to fill up their allotted space adequately and effortlessly -- the picture never feels overloaded, or as if its principals are trying too hard, a blessing in a movie climate where comedic filmmakers seem to think they have to beat us over the head, Three Stooges-style, to make us laugh.
With the help of his actors and writers, Schwimmer manages to make even the simplest, potentially dumbest gags in "Run Fatboy Run" work. When Whit pompously informs Dennis that he's going to compete in the Nike River Run, the hapless Dennis shoots back, without missing a beat, "The Whatty What What?" The line is so throwaway, so seemingly improvised, that it feels like genius. At one point Whit drags the out-of-shape Dennis to his grueling spinning class; afterward, Whit stands naked before his runty competition, liberally powdering his attributes, which we can only assume are magnificent -- the sequence is shot so we get a clear view of Dennis' eyes, widening in dismay and disbelief behind those clouds of talcum powder. It's the kind of goofy sight gag that can make you groan if it's not done properly. But Schwimmer doesn't act as if we've never seen this sort of thing before -- the fact that we know we have is part of the joke. "Run Fatboy Run" takes too long to wind down, and toward the end, it makes too obvious a grab for emotional gusto. But it deserves credit for not working us over the way so many modern comedies too. It brings us to the finish line with energy to spare, instead of leaving us feeling sapped.