Market near all time high and IPO's lined up. Bears may be itching to go short. If you have to go short, buy October 10000 puts , and build on them (shift to 10100/10200 if market keeps on spiralling). At low vix, risk reward may not favour shorting calls. Don't short futures in a liquidity driven market. Bear put spreads (October) may also be considered depending upon your risk profile and margin.