Jim Morrison was arrested in New Haven, Connecticut by the police for charges of obscenity and indecency. However, historical accounts suggest that Morrison was harrassed unnecessarily by the police just prior to the concert. According to The Doors article in Wikipedia:
"On December 9th, 1967, The Doors performed at an infamous concert in New Haven Arena in New Haven, Connecticut which ended abruptly with Morrison's on-stage arrest by local police.
The incidents leading up to Morrison's arrest in New Haven are still somewhat unclear, though it is widely rumored (most notably dramatized in a scene in Oliver Stone's film, The Doors) that Morrison was having a conversation backstage in a bathroom stall with a female companion when a police officer appeared, allegedly harassed the pair—causing Morrison to become belligerent—and subsequently maced Jim in the eyes.
On stage, Morrison proceeded to go on an obscenity-laced tirade to the audience, explaining what had happened backstage, and belittling New Haven police. It was at this time that Morrison was apprehended and dragged offstage by the police. A riot ensued which spilled from the gates of the New Haven Arena (since razed) into the streets of New Haven. Morrison was taken to a local police station, photographed and booked on charges of indecency and public obscenity."