A federal appeals court on Monday issued one of the most comprehensive rulings yet limiting police use of Tasers against low-level offenders who seem to pose little threat and may be mentally ill.

In a case out of San Diego County, the 9th U.S. Circuit Court of Appeals criticized an officer who, without warning, shot an emotionally troubled man with a Taser when he was unarmed, yards away, and neither fleeing nor advancing on the officer.

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As lawsuits have proliferated against police and Taser International, which manufactures the weapons, the nation's appellate courts have been trying to define what constitutes appropriate Taser use.

The San Diego County case is the latest ruling to address the issue.

A three-judge panel of the 9th Circuit affirmed the trial judge's ruling on Monday, concluding that the level of force used by the officer was excessive.

McPherson could have waited for backup or tried to talk the man down, the judges said. If Bryan was mentally ill, as the officer contended, then there was even more reason to use "less intrusive means," the judges said.

"Officer McPherson's desire to quickly and decisively end an unusual and tense situation is understandable," Judge Kim McLane Wardlaw wrote for the court. "His chosen method for doing so violated Bryan's constitutional right to be free from excessive force."

Some lawyers called it a landmark decision.

Eugene Iredale, a San Diego lawyer who argued the case, said it was one of the clearest and most complete statements yet from an appellate court about the limits of Taser use.

He said after Monday's decision that courts will consider all circumstances, including whether someone poses a threat, has committed a serious crime or is mentally troubled.

"In an era where everybody understands 'don't tase me, bro,' courts are going to look more closely at the use of Tasers, and they're going to try to deter the promiscuous oversue of that tool," he said.

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"Certainly the officer should be able to articulate the reason the force (was used), and a mere resistance to comply may not be enough," said Sheriff John McGinness.