NFL betting line movement is a key handicapping signal for bettors that often (but not always) implies a significant betting interest in one side of an NFL game.
One of the fundamental rules of betting is that the sportsbook is always trying to limit its liability in a game in the way it sets prices. If there is dramatically uneven betting action on one side of a bet – especially in point spread or totals markets – the sportsbook may elect to move the line.
This change in the line is referred to as line movement.
Consider a hypothetical game between the Los Angeles Chargers and the Kansas City Chiefs. If the Chiefs are priced as a 4-point favorite, there's a good chance that a high volume of bettors are going to bet on Kansas City. That may cause online sportsbooks to move the point spread to Chiefs -4.5 or Chiefs -5.'