The logic is simple. Banks know traders place their stops below pivots. So before moving the price up, they often begin the process of 'mark up' by pushing price below a recent low pivot point. Traders are forced to sell, and the banks 'bag hold'.
When the banks have their fill, they move the price back up. Vice versa for distribution.
A volume spike at the initial BOS is a good sign because it means traders are scrambling to get out, whist the bag holders greedily gobble up available stock. If you see a rapid back-and-forth exchange, price is ready to reverse hard. But at the very least, the volume following the initial BOS should be above average.
