In American football betting, underdogs are written with a plus (+), while favorites are written with a minus (-). This is true for both the NFL and the NCAA.
Football odds are written as:
USC +510
Alabama -770
This is an example of moneyline betting. In American betting, odds are described in terms of a $100 bet. Here, a $100 bet placed on USC would pay out $510 in the event of a win. The bettor is paid out a total of $610 for this win (which includes the original $100 bet).
On the other hand, a $770 bet placed on Alabama would pay out $100 for this win. The bettor would earn $100 from this bet, as well as keep their original $770. For this reason, football betting sites see more action on the underdog than on the favorite.
Point spread football lines are written as:
Cincinnati Bengals +3.5 (-110)
LA Chargers -3.5 (-110)
As mentioned above, lines detail odds in a more specific way. In this example, the Bengals are the 3.5 point underdog and the Chargers are the 3.5 point favorite. For a bet on the Bengals to pay out, they need to not lose to the Chargers by at least 4 points. For a bet on the Chargers to pay out, they need to beat the Bengals by at least 4 points.