Understanding NFL Line movements

Understanding NFL Line movements

NFL bettors attentions turn towards the regular season return in September and the sport offers a wide range of betting opportunities, ranging from straight up winners to team or match total points. However, the most popular bet remains handicap or against the spread betting, where the perceived weaker side is allowed a point start, often measured in half points to eliminate the handicap tie.

Odds of 1.91 in decimal format are typical, requiring a breakeven point of 52.4% winning bets to be successful at such prices. Although Pinnacle, price matches up at a more generous 1.952, which further reduces the success rate required to make a profit to 51.2%.

Against the spread (ATS) markets are sometimes fluid from opening quotes to kick off time, with a combination of line or occasionally price changes and so an appreciation of the dynamics of the scoring within the actual match and the impact of any price or line changes can be useful.

The NFL uses a scoring system that is heavily bias towards scores accumulating in multiples of three, the value of a field goal or seven, a one point converted touchdown. Therefore, the margin of victory in games, which ultimately decides the “against the spread” winner, is skewed to reflect this tiered scoring system. (Read the importance of 3 & 7 in NFL here).

Victory by three points is by far the most common winning margin in the NFL, occurring around twice as frequently as the next most common margin of seven.

The introduction of the option of a two point conversion has slightly tweaked the figures, but the pre-eminence of three point victories and the implication for bettors who chose to take underdogs with a 2.5 point start or favourites giving up 3.5 points and risk the favoured side winning by a field goal is clear.

Winning Margins in the NFL Regular Season 1978-2013

Margin of VictoryFrequency %
14.3
23.8
315.3
45.5
65.7
78.4
105.9
133.2
144.6
173.6

Odds movement in the days leading up to game day occur for a variety of reasons, some of which are more transparent than others. Teams are required to file regular injury reports and doubt surrounding the participation of a vital player, most notably the quarterback, can move lines by upwards of a field goal.

More commonly lines will move by much smaller margins to reflect the strength of the opening quotes, the weight and origin of betting money and the preferred stance of the bookmaker involved.

Historical NFL betting line movements

The average line movement during the regular season since the start of the 2009 season has been 1.1 points. In 23% of games the opening line was the same as the closing line, although there may have been movement before the line settled back to the original quote.

Unsurprisingly, week one was the most volatile week with a raft of new line-ups and starters, resulting in a greater level of uncertainty compared to subsequent weeks. Lines have moved by over a point and a half, on average during the opening week.

The average net line movement remains around a point for the majority of the regular season, before greater levels of divergent opinion returns in week 17, where sides may have widely differing levels of motivation or need to win.

Team selection also becomes a factor, as starters may be rested by sides that are already locked into their post season seeding position or issues may be already settled by staggered kick off times, causing late adjustments.

Although quoted odds aim to offer attractive prices without actually stepping over the line, whereby a systematic approach can consistently find value, there have been occasions where blindly selecting less popular selections, such as underdogs at home has appeared to present profitable long term results.

Even when a handicap has attempted to level the playing field, the lure of a big name, successful team is hard to resist and it is often more enjoyable to watch the more talented team eat into an artificial handicap lead, rather than side with an underdog as they are relentlessly chased down.

Therefore, there is the potential to post poor value prices or lines about unconditionally popular teams and still attract money and this may have contributed to the claimed profitable strategy of siding with unloved home dogs in the early 2000’s, as unintended value leaked to the opposite side of the line.

Alternatively, the profit from blindly betting home dogs may have arisen simply through the random nature of many sports, the NFL included. Posted lines rarely top 20 points, yet 20% of matches since 1978 have seen winning margins of 20 or more points. So the spreads are centred about an average expectation and even the most skilled of prediction is awash with uncertainty. An excessively unlucky run of such things as non- repeatable turnovers for a group of teams may temporarily distort results and ultimately ATS records.

Therefore, although we may analyse line movements from an increasingly large number of tracking sites to see if lines are moving towards or away from the breakeven points, the high levels of uncertainty should always be uppermost.

Lines move because of many, often conflicting reasons. Opening lines define the starting point, but informed or mass appeal can then move them in opposing directions, until a sport where even a whole season is insufficient for some teams to escape the vagaries of good or bad luck, produces a final score.

The profit to be made from indiscriminately siding with home underdogs has evaporated over the last five seasons. Since 2009 home dogs have won as often against the spread as they have lost, compared to a 55%+ ATS success rate in its heyday from the mid 90’s to the early 2000’s.

But we can use line movements to try to better understand why the profit may have disappeared or where it is most currently likely to be found.

An underdog that is initially receiving a four-point start could be considered to lack overall market confidence if the line then moved out to six points. Alternatively a move from four to just a three point start would indicate more confidence in their ability, especially as the line has moved onto a key number. Of course this endorsement or otherwise of the team’s likely performance on game day, may be informed or misguided or mixture of the two.

Since 2009, home dogs, when their opening line equated to the closing line or overall market confidence was apparent in the line movement, has failed to win even half of their ATS games at the closing line. In comparison home underdogs, where their handicap start has increased over the week has won ATS over 54% of the time.

Therefore, line movement can be used to identify subsets where profit has been made at closing lines, albeit at the cost of sample size and that should reduce confidence in the possible repeatable causes of the favourable outcomes.

Line movements cannot, on their own provide guarantees of profit. At best they help to illuminate a process where inevitable randomness in the actual game result may produce apparently profitable patterns that do not persist, particularly in groups that are already priced close to the break even point.

In the absence of an independent assessment of each team’s likely ability, possibly based around efficiency statistics, they can only provide ATS win percentages based on how lines reacted in the past. Those who interact to set these lines may choose to act differently in the future. Especially if a contrarian systematic betting approach becomes more widely recognised and betting habits partially change.

Line movement should be treated as a useful, additional tool to aid prediction and not as a single source with which to make a selection.

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