hello Anant.
the operative word is piercing.
In an uptrend, a green bar should pierce the upper Band and the following red bar should also pierce the upper band and should close inside the bands, (which indicates weakness in the uptrend, because price tried to move up but could not as selling pressure pulled down the price)=> this set up will give maximum pull back, i.e, generally will result in price touching lower bands.
Reverse is true of lower band piercing.
some times we see, this green and red combo in uptrend, but not touching the upper bands. in such cases pull back will be weak and price may retrace up to central line only.
These are my observations.
cheers.