Back bet
A back bet is the conventional bet that an outcome will happen, the opposite of laying it on an exchange.
Backing is the ordinary bet. The backer stakes an amount at a price and, if the selection wins, gets the stake back plus winnings of stake × (price − 1). Back 10 units at 3.0 and a win returns 30 units, 20 of them profit. A loss costs the 10.
Bookmakers and exchanges both take back bets. A bookmaker sets its own prices with its margin built in, while on an exchange the price is whatever another user has offered to lay, and commission comes off winnings instead. In matched betting the back bet goes on at the bookmaker, where the free bet or promotion is, and the exchange takes the lay.
The back price drives the cost of that cover. With the lay held at 3.1 and 2% commission (use your own rate), a 10-unit back bet at 3.0 costs 0.45 units to cover, and the same bet at 2.9 costs 0.77. A higher back price against the same lay always costs less.
In the OddsRelay feed
In the feed, back prices are the back[] array on every matched outcome, sorted best price first. Each offer carries bookmaker (a key from GET /v2/bookmakers), price and link, the bookmaker's page for the event. Each-way and extra-place offers add places and place_fraction, and dutching legs add dutch_id.
The first entry is the top price among the bookmakers on the feed, the figure an odds comparison table highlights, and meta.last_seen gives each bookmaker's last read per sport, so a tool can show how old each price is. On raw, a bookmaker quotes name and price, while an exchange quotes back_price beside lay_price.
Prices are decimal by default. Where oddsFormat=american is accepted, on each-way, extra-place, bog, 2up and raw, a back price of 3.0 is served as +200. Fractional odds are not served, so a tool that shows them converts from decimal.
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