Beating the Book: Are There Patterns in NFL Betting Lines?

Abstract

Las Vegas sports books provide two even-money bets (not counting commission, or "vigorish") regarding National Football League games- the point-spread between each pair of teams and the total number of points scored by each pair of teams (the "over-under"). Odds makers set the numbers ("lines") for these two bets almost a week in advance of the games, and they may change these numbers throughout the week as new information becomes available regarding the teams or as bettors bet unequally on either side of the line. This study examines whether there are any predictable patterns in the betting lines over the course of the preceding week that bettors could exploit to improve their expected returns, including whether it would have been profitable to try for "middles" as the betting lines changed over the course of the week. We will also note whether during the years studied any simple betting strategy, such as betting on favorites, underdogs, home teams, or visiting teams, would have been profitable.