An arbitrage rule mismatch, sometimes called mixed rules, is when the two bookmakers on an arb settle the same event under different rules. One rare result can then void one leg while the other stands, turning the arb's small margin into an ordinary bet that can lose most of what you staked.
With illustrative prices, a $250 tennis arb that makes $4.13 on a finished match loses $142.77 if the favourite retires after the first set.
Why a settlement mismatch breaks an arb
An arb backs every outcome at different bookmakers, at prices whose implied chances total under 100%, so every result returns more than the total staked. That only holds for results both bookmakers settle the same way. Arbitrage betting covers the maths, the arbitrage calculator splits the stakes, and the betting strategy hub covers the other price-based methods.
The check is a settlement grid: one row for every way the event can end, rare endings included, and one column for each leg's return under its own bookmaker's rules. If any row returns less than the total staked, you hold a bet on that ending, not an arb. Racing splits the same way: after a late scratching, one bookmaker may deduct from the whole return and another from the winnings only, as horse racing arbitrage shows.
Risk: Betting involves risk. An arbitrage or a middle only works if every bet is accepted at the price shown, and an arb only holds if both bookmakers settle it as you expected. See responsible gambling for limits and support.
A tennis arb under two retirement rules, worked
Three retirement rules are common: void unless the match is completed, result stands once a set is completed, and result stands once play has started. The NSW rule book for bookmakers authorised there (checked October 2026) uses the first: if a player withdraws, is disqualified or fails to complete a match after the first serve, single bets on it are void and refunded, and multis are recalculated (clauses 5.2.8.1 and 5.2.8.3). Tennis retirement rules explains all three.
Example: Illustrative prices. Player A is $1.78 with Bookmaker A, whose match bets stand once a set is completed. Player B is $2.37 with Bookmaker B, whose match bets are void unless the match is completed. The book is 1 / 1.78 + 1 / 2.37 = 56.18% + 42.19% = 98.37%, so $250 splits as $142.77 on Player A and $107.23 on Player B.
| How the match ends | Bookmaker A: $142.77 at $1.78 | Bookmaker B: $107.23 at $2.37 | Result on $250 |
|---|---|---|---|
| Completed, Player A wins | Wins: $254.13 | Loses: $0 | +$4.13 |
| Completed, Player B wins | Loses: $0 | Wins: $254.14 | +$4.14 |
| A player retires before a set is completed | Void: $142.77 back | Void: $107.23 back | $0 |
| Player B retires after a completed set | Wins: $254.13 | Void: $107.23 back | +$111.36 |
| Player A retires after a completed set | Loses: $0 | Void: $107.23 back | -$142.77 |
The last two rows are the mismatch: once a set is completed, the position is a side bet on which player stops. Leave aside the chance that Player B stops instead. A Player A retirement after a set in more than about 1 match in 36 then wipes out the $4.13 on average: 4.13 / (4.13 + 142.77) = 2.8%. Cover both sides at bookmakers on the same rule, or pass.
Extra time and super overs
The NSW rule book counts extra time by default unless the market prices a draw (clauses 5.1.2 and 5.1.7). It settles soccer on the score at the end of normal time, which is 90 minutes plus stoppages (clause 5.2.7.3), and leaves the super over out of Twenty20 results unless stated otherwise (clause 5.2.2.3(h)).
Example: Illustrative prices for one knockout soccer match. Team A is $1.95 to qualify with Bookmaker A, a market that counts extra time and penalties. Team B is $2.10 with Bookmaker B in a two-way market settled at full time, with no draw price, so a draw is paid as a dead heat. The book is 51.28% + 47.62% = 98.90%, so $240 splits as $124.44 on Team A and $115.56 on Team B.
| How the match ends | Team A: $124.44 at $1.95 | Team B: $115.56 at $2.10 | Result on $240 |
|---|---|---|---|
| Team A wins in normal time | Wins: $242.66 | Loses: $0 | +$2.66 |
| Team B wins in normal time | Loses: $0 | Wins: $242.68 | +$2.68 |
| Level at full time, Team A goes through | Wins: $242.66 | Dead heat: $242.68 / 2 = $121.34 | +$124.00 |
| Level at full time, Team B goes through | Loses: $0 | Dead heat: $121.34 | -$118.66 |
Pairing a to-qualify price with the other team's price in a three-way 90-minute market is worse, because the draw is not covered at all. Extra time and penalties rules shows which markets count which period.
Players who take no part
A player bet can be void if he takes no part, stand once he is named, or stand whatever happens, the all-in default in the NSW rule book (clause 5.1.1). Some rules void a whole game: that rule book refunds all bets on a baseball game when a nominated starting pitcher does not start (clause 5.2.11), while other terms let a head to head stand, as listed pitchers explains. Player did not play rules compares the types.
Example: Illustrative prices. Team A is $2.20 with Bookmaker A, whose rule voids the game if a listed starting pitcher does not start. Team B is $1.89 with Bookmaker B, whose head to head stands whoever pitches. The book is 45.45% + 52.91% = 98.36%, so $300 splits as $138.63 and $161.37, and either team winning returns $304.99, a $4.99 profit.
If a listed starter is scratched, Bookmaker A refunds $138.63 and $161.37 stays live on Team B at $1.89. Team B winning gives $304.99 + $138.63 - $300 = +$143.62, and Team B losing gives -$161.37. That position is a one-legged arb: a single bet you never chose.
Dead heats and ties
Under the NSW rule book, a tie in a market with no tie price is paid as a dead heat (clause 5.1.8): the face value is split between those tied, then multiplied by the places they fill. In a market that prices the tie, every other bet loses (clause 5.1.7), and other terms refund both sides. Dead heat rules covers the racing and sports versions.
Example: Illustrative prices for an 18-hole golf matchup. Player A is $1.95 with Bookmaker A, and Player B is $2.08 with Bookmaker B, which refunds both sides on a tie. The book is 51.28% + 48.08% = 99.36%, so $200 splits as $103.23 and $96.77, for a profit of $1.28 to $1.30 if either player wins outright.
| Bookmaker A's rule on a tie | Player A bet | Player B bet | Result on $200 |
|---|---|---|---|
| Stakes refunded, like Bookmaker B | $103.23 back | $96.77 back | $0 |
| Dead heat: half the face value | $201.30 / 2 = $100.65 | $96.77 back | -$2.58 |
| The tie is priced, so Player A loses | $0 | $96.77 back | -$103.23 |
Palpable errors and other voids
The leg that looks best is the likeliest to be called a mistake. A palpable error clause lets a bookmaker void a bet or resettle it at the price it says it meant to offer. The NSW rule book holds a quoted payout as agreed except where a computer or other technical malfunction caused the error, or there is evidence of fraud (clause 5.1.5); other bookmakers write their own test.
Example: Illustrative prices. Team A is $1.72 with Bookmaker A. Team B is $3.40 with Bookmaker B, while every other bookmaker has Team B near $2.40. The book is 58.14% + 29.41% = 87.55%, a 14.2% margin on paper, so $400 splits as $265.62 on Team A and $134.38 on Team B.
| What Bookmaker B does | Team A wins | Team B wins |
|---|---|---|
| Lets the bet stand | $456.87 back: +$56.87 | $456.89 back: +$56.89 |
| Voids the Team B bet | $456.87 + $134.38 refund: +$191.25 | $134.38 refund: -$265.62 |
| Resettles it at $2.40 | $456.87 back: +$56.87 | $134.38 x 2.40 = $322.51: -$77.49 |
Treat a margin that large as a likely error, not a windfall.
Other voids hit one leg too. Under the NSW rule book, a postponed game that is not officially scheduled to be played within three calendar days of its original scheduled completion date counts as abandoned and is refunded (clause 5.1.6), and a bookmaker may refuse any bet (clause 3.1.9).
Reading the terms before you place both legs
Under the NSW rule book you cannot cancel an internet bet once you have confirmed it (clause 3.5.2), so read first:
- Check that both prices are the same market: two-way or three-way, normal time or extra time, the same line.
- Open each bookmaker's rules for that sport, not just its general terms.
- Search them for retire, extra time, normal time, super over, take part, pitcher, dead heat, tie, postpone, palpable and obvious error.
- Fill in the settlement grid, and pass if any row loses more than the arb can make.
- Check who licenses each bookmaker on ACMA's register, then read each market's own wording, because the NSW defaults give way to anything agreed when the bet is made.
- Save the terms as they read that day, with both receipts.
Whether arbitrage is allowed at all is covered in is arbitrage betting legal in Australia; B337 does not give legal advice.
What each unchecked rule cost in these examples
| Mistake | Cost in the worked examples |
|---|---|
| Extra time rules left unchecked | -$118.66 on $240 |
| Different retirement rules on each side | -$142.77 on $250 |
| A starting pitcher clause ignored | -$161.37 on $300 if the live leg loses |
| A tie assumed to be refunded at both bookmakers | -$103.23 on $200 |
| An out-of-line price taken on trust | -$265.62 on $400 if voided, -$77.49 if resettled |
What B337's arbitrage screener leaves to you
B337's arbitrage screener covers the price side: it checks the Terminal's sports markets and lists those whose best prices total under 100%. Those are arbs on paper, so reading both bookmakers' rules stays with you.
Screener rows are part of Terminal Pro and Full Automation, and of a separate Screeners plan arranged with the team; free accounts get the count of live candidates but not the rows. No arbitrage bet is placed automatically. Each leg is yours to place in your own accounts, by hand or on Terminal Pro from the board. Bets placed through B337 use credits. Prices on the Terminal can trail a bookmaker's own, so confirm each one before the bet goes on.
Risk: Betting involves risk. Many bookmakers restrict or prohibit automated betting, third-party access and multiple accounts, so using B337 may breach a bookmaker's terms. A bookmaker can limit stakes, void bets or close an account whether you place arbs through B337 or by hand, a risk that is yours. See responsible gambling for limits and support.
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