NEW YORK (Reuters) - A grand jury decision not to indict a New York policeman over a fatal chokehold underscores how difficult it is to charge an officer in the United States, even when the tactic appears to contradict police department policy and is caught on video.

Although Wednesday's decision caught some Americans by surprise, indictments of police officers for excessive force are extremely rare for political, cultural and legal reasons.

U.S. courts have ruled that officers should have wide latitude to use physical force to defend themselves or to take suspects into custody.

"What's so shocking about this grand jury decision for most folks is that the evidence on the videotape seemed so clear, but grand jurors will very often give the police officers the benefit of the doubt," said Vincent Warren, executive director of the Center for Constitutional Rights. "They treat them not as a citizens but as super citizens."

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The U.S. Supreme Court laid out a standard for when police may use excessive force in 1989, in a civil lawsuit about a diabetic man who said he was injured during a roadside stop.

The court ruled the amount of force must be reasonable under the circumstances, such as whether a suspect resists arrest, but it also said reasonableness should be judged from the perspective of an officer on the scene, not from hindsight.