Rule 4

The Tattersalls Committee rule that lets UK bookmakers reduce the payout on winning bets when a horse is withdrawn from a race after bets were placed but too late for the market to be reformed (typically inside 15 minutes of the off). The deduction depends on the price of the withdrawn horse — shorter-priced non-runners trigger bigger reductions because their absence changes the surviving horses' true probabilities more.

Worked example: you back a horse at 3.00 in a race where another runner at 1.50 is withdrawn late. Rule 4 deducts 65p in the pound from your winnings. A £50 win that would have paid £100 in profit settles at £35 profit instead.