No it isn’t legal. Actually, trading any derivative product outside of those which trade on recognized Indian exchanges is illegal.
Under the liberalized remittane scheme, you can take out upto $275000 a year out of India to invest. It can be used to buy stocks, real estate etc. But you are not allowed to trade any margined/leveraged products.
How ?
I consulted a lawyer and it is legal , under FEMA.
Please don’t post your homemade opinions as there is too much ambiguity around this subject matter already.