What it is: Everything from musicals to time-travel stories to unscripted shows has been brought under the cop-show umbrella. Current example: "Life on Mars," ABC's remake of a BBC show where a present-day detective (Jason O'Mara in the ABC version) is smacked by a car and wakes up in 1973. Classic: It's stretching the definition of "classic," but Steven Bochco's "Cop Rock" is one of the oddest twists on the genre ever put on screen. Others: "Cops," "Rescue 911," "Ashes to Ashes"
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