The fight concerns the fact that Stradlater has gone on a date with Jane Gallagher. Holden starts to question Stradlater about what occurred on the date and he talks himself into a fury, imagining that Stradlater made sexual advances toward Jane, and possibly Jane responded to him. Holden can't stand the fact that Stradlater actually went out with Jane, because he does not have the courage to ask her out himself. He longs for Jane silently, keeping his feelings to himself.
Stradlater is dismissive of Holden's questions and this only serves to anger him further, until Holden can't help but hit Stradlater. He tells him that Jane is not the kind of girl that he should go parking with. She "Keeps her kings in the back row" a metaphor for her sexual purity.