The drawdown was predictable in shape but striking in scale. Sports contracts have represented approximately 80% of Kalshi's total trading volume since mid-2024, a structural characteristic of the platform that the World Cup sustained and extended. Polymarket's sports share surged well above its normal baseline of around 39% during the tournament. With the final whistle blown, a significant portion of active open interest simply had no new event to roll into.

The tournament's imprint on both platforms was historic by any measure. To appreciate the scale, consider that the broader prediction market industry had already reached $23.9 billion in monthly volume in Q1 2026, up 1,107% year-over-year. The World Cup amplified that already-surging baseline dramatically. Combined June 2026 volume across Kalshi and Polymarket reached $44.8 billion, a 75% jump from May's $25.66 billion. That figure spans three entities: $31.5 billion on Kalshi, $10.26 billion on the main Polymarket platform, and $3.04 billion on a separate Polymarket US entity. Across 52 dedicated World Cup markets, total prediction market volume exceeded $5.81 billion, with the outright tournament winner contract alone drawing more than $5.2 billion in combined trades ($4.1 billion on Polymarket, $1.1 billion on Kalshi). During the tournament, prediction markets captured 27% of legal US sports betting volume, up sharply from 9% at the start of 2026. Ian Moore, an analyst at Bernstein, noted that the market share gains had "put feet to the fire for these traditional sportsbooks to start offering a similar service."

The two platforms handled the tournament differently at a structural level. Kalshi spread activity across hundreds of individual match-by-match contracts and also introduced "combos," financial instruments that function similarly to traditional parlays at legacy sportsbooks. These combos broadened the demographic appeal of the platform; Kalshi's female user base grew 106% during the World Cup period, compared with 54% growth among male users. Polymarket concentrated volume in tournament-wide winner markets settled on the Polygon blockchain, a network that processes transactions at near-zero cost. That fee structure gave users in lower-income markets a structural advantage over traditional sportsbooks, particularly for users in South Asia and Africa. The on-chain settlement data reflecting the post-tournament open interest decline will be visible in coming days through platforms such as The Block's data dashboard and DefiLlama, showing the drawdown in active USDC held inside Polymarket contracts.

User growth metrics during the tournament underscored the momentum before the drop. Kalshi's daily active users grew 36% between June 15 and June 30; Polymarket's grew 12% over the same stretch. Kalshi's mobile app surpassed both DraftKings and FanDuel in daily active users on peak tournament days, a first for any prediction market platform over legacy US sportsbooks. An Apptopia analysis found that "sportsbook customers are sampling the prediction markets while prediction-market customers are staying put," with the share of DraftKings users who also opened the Kalshi app rising from 12% on June 1 to 17.4% by June 22.

The regional picture complicates any straightforward reading of the post-tournament pullback.

India offers the starkest example. Cricket-driven prediction market demand had already been building on crypto rails there before the World Cup, making the country a significant latent audience for the tournament cycle. The Indian government's Ministry of Electronics and Information Technology issued formal blocking orders against Polymarket in May 2026 under the Promotion and Regulation of Online Gaming Act, passed in August 2025, cutting off that audience just as the tournament began. Kalshi subsequently listed India as a restricted jurisdiction. MeitY later issued warnings to VPN providers as Indian users attempted to maintain access through workarounds. The 20% open interest decline therefore reflects a market that had already been stripped of Indian participation, meaning the baseline demand in that country remains unmet by any legal product.

Nigeria sits at the opposite end of the regulatory spectrum. Polymarket remained fully accessible throughout the tournament, and no federal framework currently targets prediction markets, though the Nigerian SEC's digital asset regulatory framework is still evolving and has not yet addressed prediction markets specifically. Luno Nigeria, a crypto platform with South African roots, launched a localized prediction market product earlier in 2026 in partnership with Limitless, allowing users to trade on Bitcoin and Ethereum price direction for USDC payouts. Luno Nigeria CEO Ayotunde Alabi described the fit plainly: "Many users already follow charts and news closely, forming strong views on where prices are headed."

Across the broader African continent, no regulatory body has issued clear guidance on prediction markets, a window that analysts at TechLabari noted in April 2026 could allow platforms to operate through regulatory arbitrage for the near term.

The 20% post-event contraction is a normal consequence of event-driven volume cycling off. The more durable question is what the next major catalyst looks like and who will have legal access to it when it arrives. The 2026 World Cup ran for 39 days across 39 stadiums, an unusually long window that sustained prediction market engagement at a level one analyst described as "like the Super Bowl every day." Analysts expect prediction market platforms will now compete for volume across political, economic, and lower-profile sports markets, and the regulatory geography that shaped who could participate in the World Cup cycle will continue to define those platforms' growth ceilings in the world's most populous markets.