When you hedge using a spread bet, you open a position that will offset negative price movement in an existing position. This could be trading the same asset in the opposite direction, or on an asset that moves in a different direction to your existing trade.
For example, if you were worried that inflation might impact the value of your share portfolio, you might decide to take a long position on gold – an asset that typically has an inverse correlation with the dollar and can protect portfolios from inflation. If your shareholdings did decline, the profits from your spread bet on gold could offset any losses. But if your shareholdings rose in value instead, this profit could offset any potential loss to your gold spread bet.