Starting Price or SP betting is when you back a horse or dog and do not take a price ie: you do not take a fixed betting odd. You leave your bet to be settled at the official Starting Price or SP.
The SP is the official returned price of a horse from the racecourse at the point the race started. The Starting Price is decided by ‘SP reporters’, whose job it is to give a fair and accurate official SP price that reflects the on-course bookmaker market.
You may want to bet at SP when there are no early fixed odds on the race in question or if you believe SP will return greater odds than either the early prices or the Live Show / Board Price odds.
Some online bookmakers like Bet365 Online Bookmaker offer ‘best odds guaranteed’. This means if you take an early price on a race then if the SP is larger you get the SP instead. In other words you are always paid out at the highest price, either the early price on the selection or the SP. This is a great option to have as it removes the need to agonise over whether you are doing the right thing by taking an early price on a horse or a dog.