Though a single word is not usually enough to constitute a theme in a literary work, the notion of innocence is a motif throughout The Catcher in the Rye. Holden Caulfield's reverence for childhood's innocence and dismay when he sees that it has been violated or fears that it will be informs the way he thinks and acts.
The reason that Holden gets into a physical altercation with Stradlater is because he is deeply upset at the thought of his roomate defiling Jane Gallagher, a girl he has known for some time. Jane's quirks, such as her "muckle mouth" and the way she keeps her kings in the back row when she plays checkers are part of her childlike and innocent charm. Stradlater's taunts and the fear that Jane's stepfather has acted inappropriately toward her torture Holden's thoughts.
His late brother Allie's intelligence, precociousness, and loving relationship with Holden is another source of pain to Holden. Allie has many similar, guileless behaviors to Jane; for example, he wrote poems all over his baseball glove to read when he was in the outfield of a baseball game. Allie is forever suspended in a childhood innocence in Holden's mind. Because his older brother DB has "sold out" to become a Hollywood writer, Holden feels that DB has lost his innocence. His sister Phoebe retains her innocence, and Holden feels close to her and protective of her as a result.
Sunny, the teenage prostitute that Holden encounters in Manhattan, is another source of pain to Holden. Her innocence is long gone, and Holden is both fascinated and repelled by her.
Holden is experiencing cognitive dissonance because he has recognized that he must leave behind his own childhood innocence. He is physically overgrown and even has a dash of premature gray in his hair. He sees both preserved innocence and lost innocence in the world around him and struggles to find a way to process his feelings about the contrast and what it means to his own transition to adulthood.