Double chance bet is a term used in soccer, not American Football betting. When you bet the money line (or 1×2 line), there are three possible outcomes to the game: a home win (1), a draw (x), or an away win (2).
But sometimes, you can give yourself a better chance of winning a bet, if you think a team can either draw or win.
A double chance bet means you take either the home team to win or draw, or the away team to win or draw.
Example of a double chance bet
A prime example of this came from an English Premier League match between Leicester City and Bournemouth. On the 1×2 or money line betting, Leicester City (-120) was favored over Bournemouth (+333), with the draw (+275).
If you thought that Bournemouth could get a draw, or maybe even a win on the road, you would have to bet both results on the money line, and one would automatically lose before the match started, since there can only be one outcome.
But if you took Bournemouth on the double chance line (+100), which was Bournemouth to win or draw, either result would have won your bet.