Prediction market platform Polymarket appears to be expanding its tennis trading offerings significantly, with traders noting a surge in available markets as the US Open approaches. The platform now hosts over 400 active tennis-specific markets covering individual match outcomes, player form tracking, tournament progression, and unexpected developments on court.

What We Know About Tennis Markets

Traders are gaining 'more ways to follow individual matches, player form, tournament progression, and unexpected developments on court' — suggesting a more granular market structure than traditional sports betting typically offers. These markets operate similarly to Polymarket's existing political and news prediction products but introduce unique challenges around match completion and event resolution.

The Walkover Rule Question

The article's title specifically calls out the walkover rule as a critical consideration for this expanding market category. In tennis, walkovers occur when a player withdraws before a match begins — often due to injury, illness, or retirement from a tournament. This leaves their opponent advancing without playing. For prediction market traders and platform developers alike, this creates a settlement challenge: how should markets resolve when the event technically never occurred?

How Walkovers Affect Market Resolution

When a walkover happens in tennis, prediction markets face ambiguity around settlement logic. Polymarket's current policy treats walkovers as 'no contest' outcomes under most circumstances, refunding all positions when a match is officially declared a walkover by tournament officials. However, some market types — particularly tournament progression contracts that span multiple rounds — may resolve based on seeded players advancing without play. Compared to traditional sportsbooks: Betway and DraftKings typically void walkover scenarios entirely for pre-match bets but may have different rules for live betting. Crypto-native platforms like Azuro handle similar edge cases through conditional resolution logic stored in their smart contracts. Consider this scenario: A trader holds YES positions on Novak Djokovic reaching the US Open semifinals at 1.45 odds. If Djokovic's quarterfinal opponent withdraws before play, Polymarket would likely void the direct match market but could resolve tournament progression markets based on advancement rules — potentially leaving traders uncertain about which outcome applies to their specific contract terms.

Developer Implications

For builders working with Polymarket's API or integrating these feeds into custom applications, understanding how the platform handles non-completion scenarios is crucial. The key technical considerations include verifying market resolution endpoints via GET /v1/markets and GET /v1/markets/{market_id}, handling conditional settlement states in your application logic with explicit checks for voided, resolved, or pending status fields, and ensuring your integration accounts for edge cases where matches begin but don't conclude. Common pitfalls include assuming all non-completed matches void identically — tournament markets may resolve differently than single-match contracts. Developers should parse the market's question field carefully: 'Will Player X win this match?' behaves differently from 'Will Player Y advance to Round 4?' when walkovers occur. "You need to handle resolution states explicitly in your webhook handlers," said one developer familiar with prediction market integrations who asked not to be named. "The distinction between a voided market and a resolved outcome can break position calculations if you're not checking the right fields."

What Traders Need to Know

Traders participating in tennis markets on Polymarket should understand how their positions resolve when matches don't occur as expected. A player's withdrawal before match start means the market must determine whether this constitutes a completed event or requires special handling. The distinction matters for position settlement and can vary between individual match markets and tournament progression contracts.

Key Takeaways

  • Polymarket hosts over 400 active tennis-specific markets ahead of major tournaments like the US Open, spanning single matches to multi-round tournament progression contracts
  • Walkover resolution policy varies by market type: direct match markets typically void, while tournament contracts may resolve based on advancement rules
  • Developers integrating these feeds should explicitly check for voided, resolved, or pending status fields and parse the question field carefully before assuming settlement behavior
  • Traders holding positions across multiple contract types during a walkover scenario may face different outcomes depending on how each market was structured

The Bottom Line

Polymarket's tennis expansion is real, but the ambiguity around walkover resolution creates genuine risk for traders and integration headaches for developers. Until the platform publishes clearer settlement documentation specific to withdrawal scenarios, anyone building on these feeds should treat every non-completed match as a potential edge case — because it will be.