Is fly kicking an actual method you were trained in to remove an aggressive person from their victim?
No, but there are plenty of moves that would also be termed as "aggressive" if you saw them on camera, because when you are trying to control someone who is attacking you, or resisting arrest, your life can be in danger very quickly.
Unless you've been in this situation, you simply have no idea how you would react. If I was arrested tomorrow, I would comply.
The general public has no idea what most of the Police's "clientele" are really like. In the 5 years that I served, I must have been in thousands of houses. Only TWO houses were clean with normal people. The rest were absolutely filthy, we are talking black grunge all over the kitchen, black bare mattresses on the floor, shite smeared all over the walls, no carpets, tons of drugs everywhere, cannabis plants, no one in the household working, most people beating each other up over stupid arguments over silly shite that no one can remember the next day, people drinking all day in the street if there's a glimpse of sun, gangs meeting for fights, people who don't wash for days. It's absolutely horrible and you come home stinking of it.
Why don't you sign up to be a Special? Your eyes will be truly opened to what Officers are dealing with every day.