Boston Red Sox vs. Seattle Mariners

Platform comparison

Active sub-markets

Market context

Polymarket is pricing this Boston Red Sox vs. Seattle Mariners contract at **100% YES**, which means the market is effectively treating a Red Sox win as fully locked in on USDC-settled, Polygon-based conditional tokens. For a Polymarket user, that leaves almost no two-sided risk in the price itself; the remaining question is operational, not probabilistic, because the contract only resolves from the official final game result and can stay open if the game is delayed or postponed. [1]

That near-certain reading is easier to understand in the context of the schedule history around this series. MLB and team ticketing listings show the originally planned June 20 fixture was shifted earlier in the week, with the Mariners announcing that the first game previously set for Saturday, June 20 was moved to Friday, June 19 at 7:10 pm local time, while June 20 still remained on the board as a separate scheduled game. [4][5][7] ESPN’s game listing also frames the matchup as part of a series, with Boston carrying a 1-0 advantage into the June 20 game, which helps explain why traders would anchor the contract to a specific completed result rather than to series context. [6]

The practical catalysts are the things that can still affect settlement: line-up confirmation, any further weather or calendar changes, and whether the game is completed without a suspension or cancellation. Polymarket’s own market page states trading remains open and the market stays live until the game is completed if postponed, which matters for anyone holding conditional tokens into the settlement window. [1] Recent ticketing and schedule sources indicate the game was being treated as a live scheduled event rather than a voided fixture, so the main dependency is the official final statistics once MLB records the result. [4][5][7]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We track Boston Red Sox vs. Seattle Mariners on the five venues with material liquidity for prediction markets. Live odds come from the Polymarket Polygon order book — the only source that ships real-time data under an open licence. For Kalshi, Betfair and Manifold we list platform attributes (fee, KYC, settlement, payment) instead of fabricated odds, because their APIs use non-comparable contract definitions.

Resolution & payout

Polymarket-based markets settle through the UMA Optimistic Oracle on Polygon. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution. Payouts settle automatically in USDC the moment the result is final — no bookmaker, no delay.

Kalshi-based markets settle in USD via the CFTC-regulated clearinghouse. Betfair Exchange settles in GBP/EUR net of commission. Manifold is play-money and does not pay out real funds.

FAQ

Where can I trade this market with the lowest fees?

On Polymarket UK, which mirrors the Polymarket order book at 0% fees. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

What's the difference between YES and NO shares?

A YES share pays $1.00 if the event happens, $0 otherwise. A NO share pays $1.00 if the event doesn't happen. The market price between 0¢ and 100¢ is the implied probability.

What does it cost to trade on Polymarket UK?

Zero. Polymarket UK routes every order to the live Polymarket order book; the only cost is the Polygon network fee, typically under $0.01 per transaction.

Do I need to KYC for this market?

Not under $1,500 of lifetime trading volume. Above that threshold, Polymarket UK triggers a quick verification flow that finishes in minutes.

How reliable are the quoted odds?

The YES/NO percentages are the live mid-prices of the Polymarket order book. On deep markets they move every few seconds; on thinner ones you'll see short plateaus.