My guess is a stall from a high bank turn.
The video only captures the last few seconds of flight. The WC-130 was on departure enroute to the boneyard with 9 souls on board including crew chiefs. Since it wasn’t carrying cargo, doesn’t appear to be substantially disabled structurally, and is in a spin at impact a departure stall is highly likely. The question is what caused the departure stall and subsequent spin? A boneyard bound bird is typically on waivers to fly/airworthiness, were critical systems that could have alerted the aircrew non-operative?