Typically stocks will hit 10 earlier than index, and then they can move past that after freeze.
Not all 50 have to hit, Nifty is also weighted. Plus some stocks will be past 10.
Very unlikely, but happened in covid ( We had circuit freezes then from what i remember) and also i think when congress? govt lost.
I highly doubt anyone can move Index to circuit without any real reason. Line lagi hai of people wanting to buy on dip. I think what they did was move index through stocks near close, losing money in stocks but making more in options due to difference in liquidity.
That kind of thing should be illegal ofc, somewhat unnerving to see that its possible to do this, i always thought it was not possible to make money by brute forcing in liquid markets.
But the way options expiry happens gave a loophole which hopefully will be fixed through upcoming change. I wonder if other actors are trying to repeat this.