Prop bet
A bet on a specific occurrence within an event, such as a tennis player's aces or a soccer player's shots, not the result.
Proposition (prop) bets target a statistic or event inside a match. Player props include aces, double faults, shots on target, or kills in esports; match props include total corners, first goalscorer or first blood. Because data feeds settle them, each book defines exactly which stat source it uses.
Expected value example
Tennis, illustrative: Player A over 8.5 aces at 1.83.
- Implied probability: 1/1.83 = 54.6%.
- Suppose your model says 58%.
- Expected value per unit staked: 0.58 × 0.83 minus 0.42 × 1 = 0.0614, or about +6.1%.
On a $50 stake that is an average gain of about $3.07 per bet over many repetitions, with large variance around it.
If your model said 52% instead: 0.52 × 0.83 minus 0.48 = -0.0484, a negative bet.
Why props are different
Prop markets often have lower limits and wider margins than main lines, and books update them less often. The flip side is that a thinly traded line gives you less information about the true price, so closing line value is a noisier signal there.
Settlement rules
If a player does not start or retires injured, the prop is usually void (see void bet), though rules for tennis retirements vary by book.