-6g is easily achievable in an Extra, although not much fun. A hard push out from a spin recovery would do it if you were going fast enough.
Recovery from a spin at 700 ft would get you disqualified in most competitions, where the floor is usually 1000 ft agl and the judges are pretty good at spotting violations.
I would not fly again with any pilot who did this to me, especially in a semi aerobatic aircraft like an aerobat.