How do Vegas gambling lines work for football?

The National Football League (NFL) and college football (NCAA) have different betting lines on each game. The handicap, or point spread line, is a forecast of the number of points by which a stronger team is expected to defeat a weaker one. In contrast is the money line, where the team you bet just has to win; if you bet on a team to win with the point spread, that team has to “cover” the bet. There is also the over/under line, which is the expected total amount of points of both teams combined).

Once the lines are set for the game, usually at the beginning of a new week, the lines can shift according to many factors, such as injuries, suspensions, or much more money coming in on one side of the action compared to the other.
Many times, the handicap lines for the game are less than one touchdown, or -7. If the point spread is -10 or greater, it usually means one team is much better than the other.

Here is an example from the largest favorite to cover in a long time. In 2013, the Seattle Seahawks hosted a hapless Jacksonville Jaguars team, and went off at -19.5 (Seattle had to win by 20 points or more to win the bet). The Seahawks, who went on the win the Super Bowl later that year, covered the spread, winning 45-17.

Most of the time, once the lines are set, they will shift up or down a little, before they finally sit somewhere where even money is coming in on both sides.