If a runner is scratched after your bet is accepted, the field is smaller than it was when the price was agreed and every remaining runner is more likely to win. A deduction is taken from winnings to correct for that.
The deduction is set by the scratched runner's last available price: a runner scratched at $5.00 carried an implied 20% chance, so 20c in the dollar comes off winnings. Deductions are capped at 90c. Multiple scratchings accumulate.
Your stake is never reduced. Deductions apply to winnings only.
Bets accepted after a scratching are unaffected — that price already reflected the smaller field.
Example$100 at $4.00 = $300 winnings. A rival scratched at $5.00 carries a 20c deduction. Winnings become $300 × 0.80 = $240. Total return $340.