Betting trends highlight historical upsets as 2025 March Madness lines adjust

The NCAA Division I men's basketball tournament, commonly known as March Madness, draws significant sports betting volume amid expanded legalization across 38 U.S. states following the 2018 Supreme Court decision to overturn PASPA.[1][2]

Legal wagers on the 2024 tournament reached a record $3.1 billion, second only to the Super Bowl among U.S. sports events.[3] The 2025 edition features 68 teams in a single-elimination bracket, beginning with the First Four games on March 18 and 19, followed by the 32 first-round games on March 20-23.[4]

Historical first-round upset trends influence betting patterns. No. 12 seeds hold a 16-144 record against No. 5 seeds since 1985 (10% win rate), while No. 11 seeds are 10-150 against No. 6 seeds.[5][6]

Matchup	Lower Seed Wins	Total Tournaments (1985-2024)
No. 11 vs. No. 6	10	40
No. 12 vs. No. 5	16	40
No. 10 vs. No. 7	24	40
No. 9 vs. No. 8	74 (for No. 9)	39

Johnny Avello, DraftKings director of race and sportsbook operations, noted in an interview that bets on lower seeds have caused spreads to shrink in several first-round matchups, including No. 11 South Florida at No. 6 Louisville (from 7 to 5 points), No. 12 High Point at No. 5 Wisconsin (12.5 to 9.5 points), and No. 12 Akron at No. 5 Texas Tech (9.5 to 7.5 points).[7][8]

In contrast, heavy action on top seeds has widened some lines, such as No. 2 Purdue versus No. 15 Queens (23 to 25.5 points) and No. 2 Iowa State versus No. 15 Tennessee State (23.5 to 25.5 points).[7]

Last year, the largest No. 5 vs. No. 12 spread was Clemson at 7.5 points over New Mexico State, which upset; two No. 13 seeds were single-digit favorites, but in 2025 all No. 13 seeds opened as double-digit favorites.[7][9]