The maneuver is a legitimate training maneuver called a Return To Target. However, they initiated it WAY to low, and slowed down to nearly zero forward airspeed before they turned, which you are not supposed to do. The resulting aerodynamic phenomena that occurred is called Mushing, a temporary stall condition that occurs when rapid aft cyclic is applied at high forward airspeeds. They tried to slow down, but they didn't have the altitude or power to do so. It is incredible no one died.
Did dredge have anything to do with this:)?