The dreaded rule 4. Rule 4 dictates what happens in the event of a horse being withdrawn before the race starts. Non runners as they are called affect the odds for all the other horses in the race because it’s one less horse that can win. Rule 4 is also known as Tattersals Rule 4 or just R4 for short. To be precise it’s Tattersals Rule 4c. Anyway, this post described Rule 4 and compares it to reductions that are made by betting exchanges.
If a horse is withdrawn it effects the odds of all the other runners. A horse who has better chance of winning effects the odds of the other runners to a greater extent. So, the withdrawal of a favourite has a much bigger affect on the chances of the other runners than that of a rank outsider. Rule 4 reductions are published as pence in the pound (that’s the British pound for visitors outside the UK).
Why do some people think rule 4 is unfair?
An obvious argument is that if I [the betting public] place a bet and my horse wins, why should my winnings be reduced because another horse has been withdrawn, my horse might have won anyway [even if the withdrawn horse was still running].