A cop who can't tell the difference between someone 27 and 77?
To be fair, how much reliability can the cop assume the reporting witness has? "Eyewitness" reports are notoriously unreliable. How many times must they get reports of, say, a 40-year-old short blond woman who ultimately turns out to be a 25-year-old 6-foot black man? Cops probably figure if they have a 25% match on a description then that's ballpark. That said, executing a flying tackle on someone who's not exhibiting behavior that would justify it is reason for disciplining the officer.