This is more of options margin requirement, to write options you need to meet a certain margin either via cash or shares and it usually a fraction of the total
value of the contracts, you get hit up for more if the value of the contracts deviate too far from your margin requirement.
Share on margin is like leverage in properties, say you have got 100K worth of shares and you want to borrow more against the portfolio to buy more shares
and say they allow margin of 70% you can borrow another 70K more and use 100K as collateral ...if your portillo tanks to below the 70% mark they hit you up for more cash to bring it to 70% or more and if you can't meet in 24 hours, they start dumping your
shares at market price and recover their capital...you could be wipe out and they don't care, that why when share market crash margin call will make it worse, as all the lenders start dumping shares but there isn't many buyer and it get cheaper and cheaper and cheaper
but if you have cash, you spoiled with choices with bargain basement price.
price will recovered when most margin call are done ... because when they dump shares
it fast and furious, lenders just want their money, whatever the bid price they off load them.
you gave them all this right when you sign up for margin loan.
I don't use margin, I wait for other people to get margin call then I come in and it happens every 10-15 years