A one legged arb is an arbitrage where one bet is placed and the covering bet is not, or is voided later, so what was meant to return a small margin on paper becomes an ordinary open bet.
An arbitrage backs every outcome at different bookmakers at prices that, on paper, return more than the total staked, as arbitrage betting in Australia explains.
Common causes of a one legged arb
- The second price moves before you bet it.
- The bookmaker takes only part of the stake, or none, under an account limit or a max bet.
- The market is suspended before the second leg goes on.
- One leg is voided under an obvious error clause, as palpable error explains: out-of-line prices create many arbs and are what those clauses target.
- The bookmakers settle the event under different rules, as arbitrage rule mismatches shows.
Options and costs once it happens
Example: Illustrative prices. Bookmaker A offers Player A at $2.15 and Bookmaker B offers Player B at $2.00. The book is 1 / 2.15 + 1 / 2.00 = 96.5%. Split in proportion to 1 / price, $300 becomes 300 x 0.4651 / 0.9651 = $144.58 and $300 - $144.58 = $155.42, which return $310.85 or $310.84, a profit of about $10.84.
The $144.58 on Player A goes on, then Bookmaker B shortens Player B to $1.85. At illustrative prices, the bookmaker covers return Player A's $310.85:
| What you do | Working | If Player A wins | If Player B wins |
|---|---|---|---|
| Take $1.85 with Bookmaker B | 310.85 / 1.85 = $168.03, total $312.61 | -$1.76 | -$1.75 |
| Take $1.95 with Bookmaker C | 310.85 / 1.95 = $159.41, total $303.99 | +$6.86 | +$6.86 |
| Lay Player A at $2.20, illustrative 5% commission | Lay 144.58 x 2.15 / (2.20 - 0.05) = $144.58, liability 144.58 x 1.20 = $173.50 | 144.58 x 1.15 - 173.50 = -$7.23 | 144.58 x 0.95 - 144.58 = -$7.23 |
| Leave it open | Nothing | 144.58 x 1.15 = +$166.27 | -$144.58 |
The arbitrage calculator re-splits stakes at any price. A void instead returns that leg's stake and leaves the other bet alone: if Bookmaker A voids, the $155.42 on Player B wins or loses $155.42.
Risk: Betting involves risk. An arbitrage or a middle only works if every bet is accepted at the price shown. See responsible gambling for limits and support.
Why it is the main arbitrage risk
An arb's profit is a few per cent of the total staked, while a one legged position puts a whole stake at risk. Here one failure left open costs $144.58 when Player B wins, about 144.58 / 10.84 = 13 arbs' worth of profit.
Bookmaker terms let a bookmaker limit stakes, void bets or close an account, and many restrict or prohibit automated betting, third-party access and multiple accounts; that risk is yours. Betting strategy covers how such limits shape any method.
Placing the legs, and where B337's screener fits
Check each bookmaker's stake limit, your funds there and its rules on voids, retirements and dead heats. Then place first the leg most likely to move, be cut or be refused, so a failure leaves nothing placed.
B337's arbitrage screener lists the sports markets on the Terminal whose book is under 100%. It places no arbitrage bets: you place the legs one at a time, by hand or on Terminal Pro by clicking a price, which needs that bookmaker account attached to your B337 bot on your own computer. The screener comes with Terminal Pro, Full Automation or the Screeners plan, and bets placed through B337 use credits, a per-bet usage charge on top of the plan price.
Risk: Betting involves risk. Prices on screen are read on a repeating cycle and can trail the bookmaker's own, so confirm each one in your account before you bet. See responsible gambling for limits and support. For free and confidential support call 1800 858 858 or visit gamblinghelponline.org.au.