A federal appeals court reversed itself Friday and dismissed a lawsuit by a Southern California man who was Tasered by a police officer after being stopped for not wearing a seat belt.

The Ninth U.S. Circuit Court of Appeals in San Francisco had initially ruled in Carl Bryan's case in December, saying police must have reasons to believe a suspect is dangerous before firing a Taser and can't use the weapon merely because the person is disobeying orders or acting erratically.

The court reaffirmed that conclusion Friday, setting legal standards for excessive-force suits against police who use stun guns in the Ninth Circuit's jurisdiction of California and eight other Western states.

But the three-judge panel also said - contrary to its previous decision - that the laws governing Tasers were unclear at the time of the incident and the officer would not necessarily have known that he was violating Bryan's rights.

A previous Ninth Circuit ruling referred to the Taser as a "pain-compliance" weapon and did not specify that it could be used only against someone who posed a threat, the court said.

The officer "could have made a reasonable mistake of law regarding the constitutionality of the Taser use," Judge Kim Wardlaw said in the 3-0 ruling Friday. U.S. Supreme Court decisions allow suits against police only for violating "clearly established" rights.

Bryan was 21 when a police officer in his hometown of Coronado (San Diego County) stopped him as he was driving home in July 2005.

Wearing only boxer shorts and tennis shoes, and upset for forgetting to fasten his seat belt, Bryan swore at himself as he stepped out of the car, and was shouting gibberish and banging his thighs as he stood 15 to 25 feet away from Officer Brian MacPherson, the court said.

MacPherson said Bryan then took one step toward him. Bryan denied it, and the court said the evidence indicated that Bryan had been facing away when the officer fired his Taser.

Bryan fell on his face, breaking four front teeth. He was charged with a misdemeanor of resisting and opposing an officer, but prosecutors dropped the case after the jury deadlocked. Bryan then sued MacPherson and the city.

The court said Bryan's claims, if true, would show that the officer had used excessive force. Bryan was unarmed and was not threatening MacPherson, the court said, and the officer did not warn him he might be Tasered.

Stun guns inflict severe pain and should be used be used only when substantial force is necessary and other options are unavailable, the court said.

"The objective facts must indicate that the suspect poses an immediate threat to the officer or a member of the public," Wardlaw wrote.

MacPherson's lawyer, Steven Boehmer, said the panel had set "a clear standard for Taser use," while not retroactively applying the rules to the officer's actions.

Bryan may appeal further, said his lawyer, Eugene Iredale. Any officer with common sense, he said, should know that blasting a non-resisting seat-belt violator with 50,000 volts of electricity is "clearly illegal and an excessive use of force."