Definition: In the sports gambling world, "if bet" means a wager that is placed only if a certain outcome of a seperate wager occurs. You can place a $100 wager on Team B if Team A covers the point spread. If Team A covers the point spread, the bettor has $100 on Team B. If Team A does not cover the point spread there is no bet on Team B.
Sally placed an if bet on the Sunday night football game and needed the Vikings to win in the afternoon.