It would be kinda cool to be able to initiate a PS from a BS. It should work like this: You block an opponents beam and initiate a BS. The meter pops up, and you see 2 lines, the normal middle line and another line a little bit under it. This new line is the counter-ps line. If you have enough ki when the struggle indicator reaches that line, you can start charging a beam. However, it would consume normal amounts of ki to charge the beam ON TOP OF the ki you are pumping to block the other guys beam. This would ensure that in order to do this you would need to be at full ki or be WAY stronger than the other guy.
When the indicator reaches the middle, then you have won the block struggle and can fire the beam, which initiates another PS that you will probably win, seeing as how your enemy used all his ki up during the BS. But, maybe he LET you win, betting that you would use up all your ki winning the BS and charging the beam, and has more ki leftover than you think...sneaky sneaky. pee dubya enn