Polymarket & Kalshi tennis retirement / walkover rules — verbatim (retrieved 2026-08-23)
Not advice. Rules are set per market and change; the market's own text always wins. Full write-up with code: blog.livetennisapi.com.
Settlement matrix
| Scenario | Polymarket (polymarket.com) | Polymarket US (docs.polymarket.us) | Kalshi ATP/WTA | Kalshi ITF |
|---|---|---|---|---|
| Walkover / withdrawal before the match starts | 50-50 | Last fair market price at announcement | Fair price per rules | $0.50 per contract |
| Match cancelled, not played | 50-50 | Last fair market price | Fair price per rules | $0.50 |
| Retirement after play starts (injury, default, DQ) | Advancing player wins | Awarded winner settles $1.00 | Winner resolves Yes | Winner Yes; withdrawing/forfeiting player No |
| Delayed / postponed | 50-50 if beyond 7 days with no winner | — (see venue FAQ) | Stays open, closes after rescheduled match (within two weeks) | Same |
| What counts as "started" | "the match begins" | First serve is struck | A ball has been played | A ball has been played |
Polymarket (polymarket.com) — from the market description (Gamma API, event atp-norrie-navone-2026-05-20)
If the match is canceled (not played at all), ends in a tie, or is delayed beyond 7 days from the scheduled date without a winner determined, this market will resolve to 50-50.
If the match begins but is not completed, and one player advances due to the opponent's retirement, default, or disqualification, this market will resolve to the player who advances.
If the match ends in a walkover (player withdraws before the start and the other advances automatically), this market will resolve to 50-50.
Polymarket US — docs.polymarket.us/faqs/sports-faqs, "Tennis (WTA, ATP, & ITF)"
When does a match officially begin? A tennis match officially begins when the first serve is struck. Anything happening before the first serve (cancellation, walkover, withdrawal) is treated as a pre-event scenario and Contracts settle at last fair market prices as of the official announcement. Except in the case of ITF Men's and Women's matches, cancellation, walkover, or withdrawal will resolve at $0.50 per Contract.
Mid-match retirement, default, or disqualification. If a player retires after the first serve, defaults for a code violation, or is disqualified, the market resolves on the official result declared by the governing body. Whoever is awarded the win settles at $1.00, regardless of how many games or sets were completed.
Kalshi — per-market rules_secondary (KXATPMATCH / KXITFMATCH, public API)
ATP/WTA: If the match does not occur (signaled by a ball being played) due to a player injury, walkover, forfeiture, or any other cancellation (all before the match starts), the market will resolve to a fair price in accordance with the rules. If this match is postponed or delayed, the market will remain open and close after the rescheduled match has finished (within two weeks).
ITF: … all markets will resolve to $0.50. If a player withdraws or forfeits after a match has started, that player will resolve to No.
Detecting each branch in live data
In the Live Tennis API each match carries outcome (completed, retired, walkover, default, abandoned; null until settled), event_status (Retired, Walk Over, Cancelled, Postponed, Interrupted) and withdrew. The lifecycle status only says upcoming/live/completed/cancelled. The polymarket-tennis toolkit joins the market to the match so the venue's own rule text sits next to the live state.