Seattle Mariners vs. Cleveland Guardians

Platform comparison

Active sub-markets

Market context

The underlying event is the MLB match between the Seattle Mariners and Cleveland Guardians at Progressive Field in Cleveland, scheduled for 7:10pm ET on 26 June 2026. With the crowd-implied probability locked at 100% YES for a Mariners win, the market reflects an absolute certainty that Seattle will take the game, a stance that demands scrutiny given the volatility inherent in live baseball outcomes.

Historically, similar 100% probabilities in MLB markets have collapsed when key pitchers were unexpectedly rested or when weather forced delays, as seen in the Guardians’ 6-4 opening-night victory over the Mariners in March 2026 where the Guardians won despite pre-game odds favouring Seattle[1]. Traders approaching this programmatically should model conditional orders that trigger only if Luis Castillo’s career right-handed batting average of .217 remains stable and if Joey Cantillo’s recent strikeout performance against the Astros holds[7]. A power-user would also script bots to monitor real-time lineups, as any deviation from the expected rotation could invalidate the 100% certainty.

The primary catalysts to watch include the official starting lineups announced by MLB.TV and any weather updates for Cleveland, as rain delays could postpone the game and keep the market open until completion[5]. Recent box scores show both teams averaging just over four runs per game, with the Guardians at 4.04 and the Mariners at 3.95, indicating a tight contest where a single defensive error could shift the outcome[4]. Traders must also verify if the game is played under the Phantom Fireworks promotion, which could affect crowd dynamics and player focus[8]. Any postponement or cancellation would reset the market to 50-50, a dependency that must be factored into any automated trading strategy.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We track Seattle Mariners vs. Cleveland Guardians 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

At resolution the UMA oracle takes over: a proposer posts the outcome with a bond, any token holder can dispute within two hours. Without dispute the result is accepted and the smart contract distributes USDC instantly.

On Kalshi (CFTC-regulated) resolution runs through their in-house clearing engine in USD. Betfair Exchange settles after match end in the account's local currency. Manifold pays no cash — only its in-platform "mana" currency.

FAQ

Where can I trade this market with the lowest fees?

On Polymarket Bot 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.

Is this market available outside the US?

Polymarket Bot UK is available in most jurisdictions where Polymarket isn't directly accessible. Polymarket itself is geo-blocked in the US/UK/EU. Always check local regulations.

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 Bot UK?

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

How fast are USDC deposits?

Polygon credits deposits after 12 confirmations — usually under 30 seconds. Withdrawals follow the same path and land back in your wallet within minutes.