For example, if the S&P 500 futures price is higher than the index’s price, investors can sell short the futures contract and buy (go long on) the stocks in the index. In other words, index...

For example, if the S&P 500 futures price is higher than the index’s price, investors can sell short the futures contract and buy (go long on) the stocks in the index. In other words, index arbitrageurs sell the expensive product – the futures – and buy the cheap product – the stocks.