The foreign institutional investors (FIIs) were net sellers to the tune of Rs 783.28 crore in the futures & option segment on Thursday.According to data released on the NSE website, FIIs were net sellers of index futures to the tune of Rs 795.51 crore and they bought index options worth Rs 87.68 crore. They were net sellers of stock futures to the tune of Rs 75.93 crore and they bought stock options worth Rs 0.48 crore.