Sportsbook Promotions and the Growth of Parlay Wagering

Sportsbook promotions may influence not only how much consumers bet but also which gambling products they choose. This distinction matters because multi-leg, or parlay, wagers combine multiple contingencies into a single, longer-odds wager, and prior research associates them with higher sportsbook margins and substantially larger average realized bettor losses per wager than single-leg wagers. Using approximately 547 million National Football League (NFL) wagers placed with a regulated U.S. sportsbook during the 2018-2023 regular seasons, we estimate bettor-week panel regressions with bettor and NFL week-of-season fixed effects and controls for wager count and total stake to examine whether greater parlay wagering coincides with the introductions of sportsbook bonuses, free bets, and profit boosts. Parlay wager and stake shares increased substantially in 2021 and further in 2022 and 2023, coinciding respectively with the first offering of sportsbook bonuses, free bets, and profit boosts. Cumulative 2023 panel estimates place both shares approximately 19% points above the 2018-2020 reference period. After excluding directly promotional wagers, both shares remained approximately 17% points above the reference period. Season-boundary regression discontinuity (RD) estimates based on non-promotional wagers provide complementary evidence: discontinuities in parlay wager and stake shares were negative at the start of each control season but positive at the start of each promotion-period season. The findings indicate that the 2021-2023 promotional periods coincided with a substantial shift toward parlays and suggest that assessments of the relationship between sportsbook promotions and bettor behavior should consider product choice alongside wagering participation and volume.