Dutching
Dutching splits a stake across several selections in the same market so the return is the same whichever of them wins, covering a position with back bets alone.
Where matched betting covers a bet by laying it, dutching covers it by backing the other outcomes as well. Each leg's stake is set in proportion to 1 ÷ its price, which makes every leg return the same amount. It needs back prices only, so it also works on markets an exchange does not list.
Take a two-way market priced 1.87 at one bookmaker and 2.0 at another, and 100 units to spread. The sum of 1 ÷ price is 1.0348, so the return is 100 ÷ 1.0348 = 96.64 units whichever side wins. The legs are 51.68 units at 1.87 and 48.32 at 2.0. The 3.36 units given up is the cost of the cover, set against whatever promotion made the bet worth placing. A three-way market, such as a football match result, works the same way with a third leg.
In the OddsRelay feed
OddsRelay's dutching feed type, GET /v2/odds/dutching, carries the dutches already assembled. A dutch is one back leg per outcome of the market, and every leg's back[] offer carries dutch_id, eight hex characters naming the dutch it belongs to. A tool groups one market's offers by dutch_id and computes 100 ÷ the sum of 1 ÷ price for each group. There is no lay on this feed type, and a leg can be an exchange's back price as well as a bookmaker's.
Group by dutch_id, never by the line. On a totals market a whole-number or quarter line can pair with its half line, Over 2 with Under 2.5, so two legs with different point values can belong to one dutch. A bookmaker that is a leg of two dutches appears once in each.
Dutching is served in decimal only, and a bookmaker filter keeps a dutch only when every one of its legs is a named bookmaker. A tool that would rather build its own combinations from every bookmaker's prices can use GET /v2/odds/raw instead, where each bookmaker's outcomes for an event arrive side by side.
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