Sure bet (surebet)
A sure bet, or surebet, is another name for an arbitrage: prices on every outcome of a market whose implied probabilities add up to less than 100%.
Many arbitrage tools use the word, and the test is the same. Take a football match result priced 2.30 on the home side at one bookmaker, 3.60 on the draw at a second and 3.90 on the away side at a third. Their implied probabilities are 43.48%, 27.78% and 25.64%, 96.90% in all. Of 100 units, 44.87 on the home side, 28.67 on the draw and 26.46 on the away side return the same amount whichever outcome wins.
The word describes the arithmetic at the prices shown, not what happens when the bets go on. The legs are struck one at a time at different bookmakers, and any price can move before the last one is placed. A bookmaker can accept less than the stake asked for, or void a bet under its own rules, which leaves the other legs uncovered.
Every outcome needs a leg. Two legs on a three-way market leave the draw uncovered, and on line markets every leg must be on the same line, so Over 2.5 goals at one bookmaker pairs only with Under 2.5 at another. A mismatch of either kind lines up two different bets.
In the OddsRelay feed
In OddsRelay's feed a sure bet is something a tool finds, never a field. On the matched feeds each outcome of a market arrives once, with every bookmaker's price in back[], best first, so the back[0].price of the home, draw and away outcomes are the three legs of a match result. On GET /v2/odds/raw, where each bookmaker keeps its own outcome labels, the tool matches the selections up before it adds anything.
Each leg's age matters as much as its price. meta.last_seen gives each bookmaker's last read per sport, so a tool can show how old the oldest leg is, and every product has a maximum update time of 10–20 s.
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