To trade in derivatives the exchanges ask for margin, i.e., SPAN + Exposure, to carry forward positions overnight. Until now a short margin penalty of up to 5% would be applicable if the margin available in your account went below the prescribed SPAN margin. SEBI as part of its risk management measures has mandated that w.e.f. 1st June 2018, short margin penalty will be levied if the full margin (SPAN + Exposure) isn't available in the trading account. Read more here.