Short index futures can make a portfolio delta neutral by offsetting the directional exposure to the underlying asset. However:

• Delta neutrality only works for small price movements
• Large moves will cause the delta to change (due to gamma), requiring rebalancing
• Short futures do not provide protection against large moves because gamma risk remains
• Gamma represents the rate of change of delta with respect to the underlying price

Therefore, while short index futures can achieve delta neutrality, they do not help with large moves in the underlying asset.