I am not sure if this is any help in this situation, but this is the closest thing I have found to a definition of the 180.
10.5 Match Disqualification –Unsafe Gun Handling
10.5.2 If at any time during the course of fire, a competitor allows the muzzle of
his handgun to point rearwards, that is further than 90 degrees from the
median intercept of the backstop, or in the case of no backstop, allows
the muzzle to point up range, whether the handgun is loaded or not
I am guessing that the side berm would now be the backstop.