punta,

It's basically the same as line betting, except that both teams are handicapped by an extra 2 points. (Brisbane -3.5 instead of -1.5, St George -0.5 instead of +1.5) As a result, instead of Tab Sportsbet's regular $1.85 for "line" betting, the price is usually around $2.00. (St George are actually much shorter in the game you mentioned, but that's because there's been a plunge on them)

As a result of the extra 2 points handicap, there are actually 4 possible results, where a bet on neither team wins and the bookie scoops the pool. For example, in that St Geo/Bris game, if Brisbane wins by 1, 2 or 3 points or the game is drawn, then no punter would win.