The 3 Biggest Causes of Line Movement in Sports Betting

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Many betting sites released odds for Week 1 of the 2018-19 NFL season with weeks to go before kickoff. Betting lines for a season-opening Thursday Night Football clash between the defending Super Bowl champion Philadelphia Eagles and the visiting Atlanta Falcons opened with the Eagles favored almost by a full touchdown in the point spread.

Cut to a fortnight later and the game’s consensus point spread is almost a pick’em. The Atlanta Falcons are currently only a (+1) underdog as the fateful hour approaches.

By the time you are reading this, it is most likely that game will be over, and we will already know whether bettors should have been putting cash on the “Iggles” or the Dirty Birds.

But the question remains – how did it happen? What are the possible causes when a betting line moves substantially, making a favorite into a toss-up hopeful or even an underdog? Or an even more-pronounced favorite?

Let’s talk about the biggest causes of line movement.

Analyzing Line-Movement: The Action is Always Key

Keep in mind that whatever affects line movement, the betting action always plays a role. A sportsbook’s odds manager can re-set the lines on a daily basis, but by the end of each day’s action, the wagering will influence him to shorten, lengthen, or sit pat.

Occasionally a house bookie might allow heavy action on a given bet to continue without changing the payoff lines or the point totals very much. If the casino’s handicapper is convinced that the Dallas Cowboys are going to win on a given Sunday, then hey, let ‘em all bet on the New York Giants all they want. It’s like selling a hotcakes-volume product for free with only a small amount of risk.

But for normal lines, the sportsbook will tend to want “balanced” action – or close to 50% wagers placed on either side of any market. That ensures that the house is safe no matter how the day’s games, matches, and tournaments turn out.

In horse racing, the action drives the odds almost completely. In football, baseball, basketball, and soccer, the action is like a politician’s approval rating, a hidden hand underneath the surface. If something other than the action affects lines, they’re likely to be affected yet again (even in a subtle way) by the way bettors react to the changes.

With that out of the way, here’s our top 3 line-movement causes and an honorable mention.

Line-Movement Cause #1: Popular Bets (Both Good and Bad)

Following Super Bowl LII in February 2018, I was congratulated by fellow handicappers on successfully “predicting” the outcome – a win for Philadelphia. I had told my readers to pick the Eagles on the moneyline or against the point spread.

Except I didn’t deserve their congratulations, because I didn’t actually predict the winner. I had absolutely no idea who was going to win. That was the point.

When what appears to be a toss-up battle is posted on a sportsbook with one side a clear favorite, as the Patriots were when they faced Philly for the NFL title, the choice is clear…gamble on the so-called “underdog” and promise yourself the better payoff if they win.

Experienced handicappers urge bettors to bet against the public, which usually means betting against favorites (such as the Pats in Super Bowl LII). Recreational gamblers tend to pick moneyline and point-spread favorites a little bit too often because nobody likes to lose a bet.

If a (+2000) or 20-to-1 underdog would be likely to win 2 or 3 games out of 20 against a favored opponent, then they’re a good team to bet on under those circumstances. If you bet on 20 (+2000) underdogs who each have a 1-in-10 chance to win straight-up, then you’ll likely wind up with at least 2x as much money as you began with.

But that’s not the way a one-time lark bettor thinks when he’s putting 50 bucks on the Super Bowl. He’s just trying to pick a winner. As a result, the relative lack of action on most underdogs tends to make them slightly under-valued in the odds over the long haul.

However, since over-confident betting action on the favorite can only

Line-Movement Cause #2: Injuries

You don’t have to be an experienced bettor or handicapper to know that an injury to a star performer can change a sportsbook’s odds for a game, match or tournament.

However, it does take some experience and savvy to dissect injury news. Each sport tends to have its own characteristics when it comes to how much is revealed (or not revealed) about injuries. Vegas bookies must weigh several factors when an injury to a goalie, a quarterback, a point guard or another key college or professional athlete is not at 100% or likely to be unable to play.

Most soccer “injuries” are fake, which is to say that when you see a player rolling around on the pitch holding their knee and wincing in pain, they might be hurting temporarily, but there’s 1 chance in 10 that it’s anything serious or permanent. If the footballer’s squad is leading the match and he or she is trying to kill time, make that 1 chance in 100.

The NHL’s culture is well-known when it comes to injuries. In the regular season, coaches and trainers typically tell the truth, but good luck getting them to offer a real opinion on when a player will return. In the Stanley Cup Playoffs, however, all bets are off (excuse the pun). Teams will report that an injured player as “a cold” or “the flu.” Players do occasionally get sick in the playoffs, but 90% of the time, “the flu” means a busted arm, leg, rib, or another serious injury.

Football, basketball and baseball injuries tend to be more readily-apparent when they happen. But understanding how a key injury will affect line movement depends on knowing how expected less-than-100% performances change the likely outcome of an event.

Principles of Line Movement due to Injury

The more players on the field, pitch, rink or court at one time, the less an injury is likely to affect the betting lines overall. If France is a heavy favorite to beat Algeria in a FIFA match, and Kylian Mbappe sprains his ankle, the French should still be prohibitive favorites even after the report comes out. (Remember, soccer is played 11-on-11.) However, Mbappe’s proposition-bet lines will certainly change.

Most bettors know that a starting quarterback is the most important player on an NFL gridiron. But remember that a middle linebacker – or a safety – can be considered the “quarterback” of a defense. If Aaron Rodgers goes down with a broken arm, moneyline odds on the Green Bay Packers are likely to lengthen dramatically. If interior LBs Blake Martinez and Oren Burks go down (or star edge-rusher Clay Matthews) it is unlikely to affect the betting action as much, and therefore the lines won’t move as much. But it could be an equally lethal blow to the squad’s chances.

Finally, consider what is being asked of an athlete who announces that he or she intends to play through an injury. If Tiger Woods suffers yet another back injury before a tournament but doesn’t withdraw, what is the golf course like? If it’s a hilly course with thick rough and tremendous hazards, Tiger is likely to aggravate his ailment during the course of 4 rounds, and his futures line-to-win is likely to move a lot. But if he gets to ride around in a cart while playing in an exhibition on a flat desert course, his chances to win might be able the same, and if the line moves it’s thanks to pessimistic fans and not the bookie.

An injury can affect the O/U total in a contest. Suppose an NBA point guard who specializes in driving to the basket suffers a knee or ankle injury but suits-up anyway. A resourceful passer and shooter can still lead a team of cagers to victory in that scenario, but not by pushing the tempo and risking everything for a few easy buckets. Therefore, the team will be expected to slow the pace and play an outside-inside game with longer possessions, meaning that the Vegas point total should tick downward.

Line-Movement Cause #3 – News and Reporting

It would be a mistake to claim that the media controls betting odds and line movement. After all, bookies base odds on trends, scientific analysis and wagering action. Vegas professionals know to ignore tabloids and reckless blog hype – even the reckless hype on the blog you’re reading now.

But the sports media still has a major role to play, influencing how bettors and handicappers think. For instance, the 2018 Grand National was won by the (+1100) underdog Tiger Roll. Tiger Roll is an excellent “jump” race Thoroughbred and posted several terrific wins and top-3 finishes in the year leading up to the race at Aintree.

But the animal was only 8 years old, and most Grand National winners are 9-year-olds. The media jumped on the discrepancy, reporting on the “curse” that supposedly prevents the more younger horse from winning the Biggest Race of All. As a result, the horse’s odds moved slightly longer than they would have if bettors were evaluating the contestants free of bias, and those who ignored the media and bet on Tiger Roll received a bigger payout when he won.

It was a case of a line that should have moved shorter, but the line’s relative lack of movement created the opportunity for savvy bettors to clean up.

Honorable Mention: Fake News and Reporting

Occasionally a line will move based on erroneous reporting that influences bettors and even sportsbook odds-managers to change their tactics.

One example would be the pessimistic and impatient attitude of the media toward Tiger Woods’ comeback in 2018. Early in the year, Tiger was considered a futures-odds favorite for the Masters Championship, as well as a favorite in advance-wagering on the U.S. and British Opens and the PGA Championship. But Woods was too inconsistent to win in the first 3 majors, and some reporters (many of whom have simply grown to dislike Tiger’s attitude over the years) declared that the cumulative effect of injuries and the aging process should rule out the 42-year-old as a serious contender.

Tiger’s odds to win the PGA Championship grew longer, to (+2800). But he made a thrilling Sunday charge at the tournament in St. Louis and almost won, paying-off for prop bettors who gambled on Woods finishing in the top 3 or the top 10.

Then there was the strange case of the Men’s Ice Hockey tournament at the 2018 Olympic Games in PyeongChang. With NHL players sitting out, Team Russia appeared to be the heavy betting favorite thanks to Kontinental Hockey League stars like Ilya Kovalchuk and Nikita Gusev. But when the IOC censured Russia and stripped its flag before the Games, the American and British media reported – based on very little evidence – that the KHL would likely boycott the Games in retaliation.

As a result, the gold medal futures line on Russia – now known as Olympic Athletes from Russia – grew as long as (+300) at some sportsbooks despite Team Canada, Team Sweden and Team USA competing with journeymen. But smart international hockey fans knew that there was no way Vladimir Putin (himself a gigantic hockey fan) would allow Kovalchuk and other legends to sit out the Olympics.

As it becomes more apparent that the Associated Press and BBC were guilty of wishful thinking, the consensus gold medal futures market for Olympic Athletes from Russia grew shorter, to (+200) to (+150) and finally to (-100). But bettors who had already bought-in at 3-to-1 payoff odds didn’t mind at all. OAR won the gold medal in thrilling fashion, and those with a winning bet slip that was placed a suitable length of time before the Games in Korea owed the media a thank-you bouquet.

Conclusion: Know the Specifics in Each Sport

I have only touched on a few of the major causes of line movement. But there are more. Many causes of upheaval in betting lines are specific to particular sports, meaning that successful bettors must understand how their favorite leagues are affected by each factor.

For instance, the weather is a huge factor in O/U total line movement in American football and soccer. Rain can actually quicken the pace of a soccer match, but it typically slows-down the pace of a football game. Therefore, nasty weather can cause the O/U total to trend up for a FIFA event but cause gridiron totals to shrink.

It’s also important to know which leagues and competitions will postpone due to bad weather, and which will play on no matter what.

Baseball is a prime example of a contest that is always postponed in heavy rain. Indy car racing in America only ever takes place on a dry track. If there’s been any rain during the day and the track is the slightest bit damp, the race will be delayed. But in Formula One racing? Rain or shine, the cars will be lined up for the flag at the promised start time.

Get to know the causes of line movement and learn when to place the most-favorable bets when the lines shift. General sports knowledge is great, knowing how Vegas operates is even better. But there’s no more important weapon in the successful bettor’s arsenal than an understanding of why lines move…and how to take advantage when they do.