“gamma is one of the larger sources of non-fundamental economic activity in global markets. Market makers who delta-hedge their option positions are economically driven to trade substantial amounts of underlying shares or futures, strictly as a result of the price of the underlying itself changing, not as a result of fundamental news and without regard to the liquidity available. As a result, gamma can cause markets to overreact to fundamental news (short gamma) or too under-react to fundamental news (long gamma).”