Understanding reverse line movement (RLM) is an absolute necessity for any bettor who has designs on long-term success, and knowing how to use it to your advantage can make it a key tool in your handicapping kit.
To understand RLM we must first understand why bookmakers move lines and prices. Bookmakers set and then adjust lines, in theory, to get 50% of action on both sides. With the house taking a cut of each bet, a pure book with equal action on both sides of the same number ensures it cannot lose.
In practice, this bookmaking nirvana almost never occurs. Oddsmakers attempt to anticipate the market when setting opening lines and then typically adjust based on the amount of betting action on one side or the other. This makes logical sense. A significant amount of money on one side should move the line in favor of that team if bookmakers are looking to get equal action on both teams.
For example, if the Eagles are favored by 3 over the Cowboys and are getting 80% of betting action, most books will move Philadelphia to -3.5 or perhaps even -4 to entice bettors into backing Dallas.
There are times, however, when the line movement goes against the weight of betting action. Using the above example, 80% of the money may be on the Eagles -3, yet bookmakers move the line to Eagles -2.5. This is known as a reverse line move.
The reason behind this is simple: not all bets are created equal. Most recreational bettors are uninformed and their wagers alone — regardless of size — won’t shift a line. Some bettors, though, with a history of winning or making wagers at the top of the market (ie sharp bettors) garner tremendous respect from bookmakers and typically move lines, even against a significant weight of money.
Again, using the above example, a majority of public bettors may have gotten down on the Eagles -3 for, say, a cumulative $100,000. But since the public has a history of either losing or not taking the best numbers, the bookmaker is happy to leave the line at -3. But if even a small-time sharp comes in with a $2,000 play on the Cowboys at +3, that could be enough for the bookmaker to move the line to 2.5.
At its essence, reverse line movement is an important tool to leverage because it cuts through much of the noise to reveal which teams sharp and/or professional bettors are taking and at what number. This is particularly true if other factors that could shift the line — such as injuries or weather — can be ruled out as the driving force behind the move.
While bettors should never blindly tail reverse line movement, it is a critical tool in handicapping that should boost your confidence if you already liked the side of the movement — or perhaps push you to reduce your bet or pass altogether if the move goes against the side you were ready to play.