A half-ball handicap is a handicap used in sports betting to balance the two competing sides and erase the opportunity of three-way betting. This betting market removes the draw option for a bettor and instead the bookmaker gives a +/- handicap to each team, usually a negative handicap to the favourite and a positive handicap to the underdog.
For example, if Team A are -0.5 they start the game 0.5 goals behind Team B. If you place a bet on this selection, Team A would have to win by at least one goal for you to receive a payout. A draw or a loss would result in you losing the bet and your stake.
If you were to place a bet on Team B at +0.5, they would start the game 0.5 goals ahead of Team A. If Team B lose, then you lose the bet and your stake. If you were to back Team B and they won, you would receive a payout. You would also receive a payout if the game ended in a draw as Team B started 0.5 goals ahead of Team A.