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Racing glossary
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You do not need to be a racing expert to take a seat — but a few terms help when you read strategy sheets, guidance, or results. Education only; not advice.
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Odds deductions after a NR
Rule 4 (Tattersalls Rule 4) is the industry rule that adjusts odds when a horse is withdrawn after a market has formed. It exists so remaining runners are not overpriced relative to the money that had been on the non-runner.
In practice: if a withdrawn horse was a short price, bookmakers apply a deduction (often quoted in pence in the pound) from winnings on bets struck at the earlier odds. The bigger the withdrawn horse’s price influence, the larger the Rule 4. Very long-priced withdrawals may attract little or no deduction.
On the exchange, markets are usually suspended and re-formed when a runner is withdrawn; matched bets on the non-runner are void, and new prices apply for the reduced field. Exact treatment depends on whether you were backed before or after the withdrawal and on exchange rules.
Rule 4 does not mean “pick another horse with the same stake.” See also non-runners.