This type of bet is used for both rugby union and league matches. The bookmakers offer prices on how many points one of the teams will win by.
For example, Leeds Rhinos will play Warrington Wolves, with Leeds as the favourites. It is easy to see by what margin the bookies think Leeds will win by looking at the handicap offered - in this case Warrington are offered a +6 handicap.
The bookies split the various possible winning margins into sections - so Warrington to win by 1-5 points, 6-10 points, 11-15 points and so on up to around 46-50 points.
As Leeds are predicted to win by a goal difference of 6, it follows that the shortest priced bands in this case are Leeds to win by 6-10 points (9/2). The bookmakers predict that it will be a close match, as the next shortest odds are for Warrington OR Leeds to win with a margin of between one and five points (odds 5/1). Any injury time counts (but not extra time) for the purposes of these bets.