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BT SCH is back turn chief hold, and should only be known because the B can launch them over you, and you can get a auto horizontal parry for a few seconds when you first enter it.
BT SSH is back turn side hold, and should only be known because you can do SSH over and over again to hop towards an opponent while back turned, and BT SSH A+B is a decent low.
The backturned stuff is really for general knowledge, sieg isn't voldo, so fighting in back turn is very dangerous, however for the times where you end up with your back turned to the opponent, there are some things you can attack them with aside from the normal back turned attacks.