Basis
The basis of a reverse bet is what is known as an "if bet." In an "If" Bet, you bet one Team A (to win, tie or cancel the match or game). If you win the bet, you then bet an equal amount on Team B (to win, tie or cancel). Essentially, an "If" bet it two bets combined into one: "If Team A wins/ties/cancels then bet on Team B to win/tie/cancel."
Definition
While an "If" bet is two, contingent bets, a reverse bet is two combined "If" bets. This bet says not only do you want to bet on Team B if Team A (wins, ties or cancels) but also that you want to bet on Team A if Team B (wins, ties or cancels).
Betting
Place your reverse bet by telling the clerk taking bets that you want to place a reverse bet on Teams A and B.
Risks
If both Teams A and B lose, you will lose as much money as if you had placed a single "If" bet on teams A and B. For example, if you bet $50 on Team A, you would lose $50 and no further money would bet on Team B. Furthermore, you would lost the $50 bet you made on Team B (for a total $100 loss) and the "If" bet would end there as well. According to SBG Global, "the maximum risk involved is twice the highest risk of your two bets." Thus, the maximum risk is $100.
Benefits
If you place a reverse bet and both Teams A and B win, you stand to win twice as much as a single bet on each team. Using the same, two-$50 bets, we can see that (at 1:1 odds), you will make $50 when Team A wins. Your "If" bet continues and you will make another $50 on Team B (for $100). The reverse bet will provide you with another $100 when Team B wins ($50) and your bet continues for Team A who wins as well ($50). You win a total of $200 for your reverse bet.