a groundloop is when the cog tries to overtake the point that drag/braking can be said to act through.
tail draggers with mains forward of the cog, yes.
tricycle types with mains aft of the cog and betw 3 points of contact, not so much.
sufficient loss of traction in the pissing wet will turn a metro into a 5T weathervane and gravity will take it downslope but it aint what i was taught to be a groundloop