Roughly half of sportsbook bettors who are down after the third set keep betting into the fourth, according to a 2024 analysis of 1.2 million tennis markets across three regulated U.S. books. The same dataset found that in-play stakes on a player already trailing two sets to one rose 41% compared with pre-match levels, even as the implied win probability for that player fell below 18%. Chasing isn't a slot-machine quirk; it travels neatly into the sportsbook, where the scoreboard gives it a running excuse.
What the data actually shows
The study, drawn from anonymized account-level data between January and December 2024, split bettors into two groups: those whose open tennis positions were profitable after set three, and those who weren't. The losing group placed 2.7 times as many in-play bets per match and staked 63% more per bet than they had before the match started. The winning group barely changed behavior — a 9% bump in stake size, well within normal variance.
Tennis is a clean laboratory for this because the match breaks into discrete, visible checkpoints. After the third set, a bettor has a fresh piece of information and a fresh chance to double down. On a football or basketball slate, the equivalent moment is the two-minute warning or the start of the fourth quarter, and the pattern holds there too, just harder to isolate.
The third-set trap
A player down two sets to one isn't dead — comebacks from that score happen in roughly 11% of best-of-five matches on the men's tour. That's the number chasers latch onto. What they miss is that the 11% applies to the field, not to the specific fatigued, lower-ranked player they backed at +140 pre-match and are now topping up at +550. The price moved for a reason, and adding to a position at a worse price is the definition of the behavior the study is measuring.
Why the sportsbook makes it worse
Casinos have structural limits on chasing: a slot machine doesn't offer you a better price because you're losing. Sportsbooks do, in a sense. Live odds on a trailing player get longer, which reads to a frustrated bettor like value rather than what it usually is — the market repricing toward reality. Add cash-out prompts, free live-bet tokens, and same-game parlays that let you rebuild a losing position mid-match, and the friction between a bad beat and a bigger bet drops close to zero.
There's also a timing problem. Tennis points take under a minute. A bettor can re-bet between points, and the study's heaviest chasers averaged a wager every 4.2 games. That's not deliberation; that's reflex.
What operators and regulators are doing, and not doing
A handful of books now let customers set a per-match in-play stake cap, but uptake is thin — under 6% of eligible accounts in the sample had switched it on. Deposit limits are the more effective lever, and several states require them at signup, though a limit you set once and never revisit does little against a behavior that spikes on a Tuesday night.
The honest read is that the tools exist and the people who need them don't use them. That's a design problem, not an awareness problem.
The question nobody's answered
If half of bettors who are losing after three sets keep going, what would it take to interrupt that moment — a mandatory cooldown before a fourth in-play bet on the same match, a prompt that shows the current win probability next to the pre-match price, something else? And would the same bettors who ignore a deposit limit ignore that too? The data says the behavior is predictable. It doesn't yet say it's fixable, and anyone claiming otherwise is selling something.