comp_sci_kid

I assume you buy 10 contracts at $100, put $50 in initial margin
price goes to $97 (you have $20 which is below maintenance margin amount of $30 you need to fill it up to initial margin) add $30 (you have $50 on the account which is equal to the initial margin). If you sell short 10 contract at $100, price goes to $103, then you get a margin call of $30.