Spread betting rewards and punishs according to how right or wrong you are with your bet. This makes spread betting risky as it can involve big losses, but also big wins. Spread betting is different to a lot of other types of gambling in that you can lose a lot more than you staked.
Spread Betting Online: Spread betting firms look at an event set the "spread". They then invite bettors to buy or sell the spread for a certain amount of money. For example, if a betting company thinks that a cricket team will make 245 runs they might quote 240-250 as the spread. If you think that they will make less than 240 runs, you would sell the spread. If you think that they will score more than 250 runs, you would buy the spread.
If you sold the spread for £10 a run, and the team made 230 runs, you would win the difference between the result at the lower spread figure, multiplied by your stake: 240 - 230=10 x £10 = £100. But, if the team made 260 runs, you would lose the difference multiplied by your stake: 260 - 240 = 10 x £10 = £200. The same principle applies if you had bought the spread.