BANK NIFTY gaps up succumbs at the target 7

one mere lesson at this late stage of this rally we should not buy any gap up.
it closes below 5 dma.
what attributes to this fall.is it expiry related or c wave of abc correction it can be clear by tomorrow.
FII figure is not bad, usa market is ok..
if it closes below 20 dma really it will be alarming.
even asia pacific index is positive today
happy trading.