This market is about the performance of horses in individual races, awarding points according to where they finish.
The points structure varies according to how many runners there are in a race, so for races with up to 12 runners the points are as follows: 1st = 50 points, 2nd = 25, 3rd = 10, any other place = 0. Races with over 12 runners taking part score as follows: 1st = 50 points, 2nd = 30, 3rd = 20, 4th = 10, any other place = 0.
This market gives you the opportunity to back or oppose a horse, something which a traditional fixed-odds betting market does not offer.
Here's how it works in practice.
In the 2004 Derby Sporting Index priced North Light at 9-12 points, reflecting their belief that he might well make the frame. If you had fancied him to do well, you might have bet high at 12 for say £2. The record books show North Light actually went on to win the race and therefore Sporting Index allotted him 50 points. So, had you gone high at 12 you would have won 38 times your stake: (50 - 12) x your stake = 38 x £2 = £76. But, had North Light not finished in the frame he would have been awarded 0 points, so the same bet would have lost you 12 times your stake: (0 - 12) x your stake = -12 x £2 = -£24.