Defendor is a superhero dramedy which premieres at the 2009 Toronto International Film Festival. Written and directed by Peter Stebbings, and starring Woody Harrelson and Kat Dennings, the story centers around three characters: an everyday guy who comes to believe he's a superhero, his psychiatrist, and the teenager he befriends.
Here is the official plot synopsis:
Reality intersects with delusion in the mind of Arthur Poppington