[Ol' Dan Tucker]

That ain’t no crop duster. Banking hard at slow speed? Not enough lift and stalled?

From the video it looks to me like they got too slow which induced a stall. This developed further into a spin.

The single frame with the deep bank angle shows the beginning of the spin.

[BwanaNdege]

Classic “approach turn stall”!

“Lower the nose
Level the wings
Full power!”

to recover.