At the start of a Leeds v Newcastle match Sporting Index
may make Newcastle favourites to beat Leeds by 0.2 - 0.5 goals.
You predict a Newcastle win and place a £10 per point
BUY (i.e. to win £10 per point greater than 0.5).
If Newcastle scored two early goals the score may be Newcastle
2-0 Leeds after 32 minutes. The new spread for the match at
this time may be quoted as 2.4-2.7.
To close your position (and take a profit) you should SELL
£10 per point at 2.4. You total profit will therefore
|| = Stake * (sell price - buy price)
||= £10 * (2.4 - 0.5)