Case Study: Tracking Line Movement in NFL Week 1

Executive Summary

NFL Week 1 represents a unique laboratory for studying betting market behavior. It is the only week of the regular season where the market must price games without the benefit of current-season data, relying instead on preseason projections, offseason roster changes, and stale information from the previous season. This case study follows the line movements of six selected games from a synthetic NFL Week 1 slate, tracking each game from the release of opening lines through the closing number. We analyze the sources of line movement --- sharp action, public money, injury news, and weather updates --- and evaluate whether early-season markets are less efficient than mid-season markets. Through detailed tick-by-tick line tracking and Python-based analysis, we demonstrate that Week 1 lines move more than the season average, that sharp bettors are more active early in the week, and that Closing Line Value is achievable for bettors who act early on well-researched positions.

Background

Why Week 1 Is Different

Every NFL betting week involves the same basic process: sportsbooks release opening lines, bettors wager into those lines, the lines move in response to the weight of money and information, and the market converges on a closing number that represents its best estimate of the true probability. But Week 1 is fundamentally different from every other week for several reasons.

First, there is no current-season performance data. The models that sharp bettors and sportsbooks use to generate power ratings are built on projections rather than observations. Preseason games provide limited signal due to starters' limited playing time. This means that the opening lines for Week 1 carry more uncertainty than any other week.

Second, roster turnover is at its peak. Free agency, the draft, retirements, and training camp injuries have reshaped every team since the previous season. The market must estimate the impact of dozens of personnel changes on each team's expected performance, a task that involves significant subjective judgment.

Third, public perception is heavily influenced by narratives --- which teams had exciting offseasons, which quarterbacks are generating buzz, which teams are expected to regress. These narratives create systematic biases in public betting patterns that may diverge from sharp money.

Fourth, Week 1 lines are posted earlier than any other week's lines, typically months in advance as "look-ahead" numbers that are refined as the season approaches. This extended market life means more opportunity for information to be incorporated but also more time for the line to be influenced by noise.

The Data

For this case study, we tracked the lines of six synthetic NFL Week 1 games from the moment of opening through game time. The data includes timestamped line snapshots from four sportsbooks (labeled Sharp Book A, Market Maker B, Retail Book C, and Retail Book D), along with simulated bet percentages and money percentages compiled from a hypothetical consensus service.

The six games were selected to illustrate different patterns of line movement:

The Analysis

Game 1: Kansas City at Buffalo --- The Sharp Favorite Move

The opening line of KC -1.5 reflected uncertainty about Buffalo's offseason quarterback controversy and Kansas City's expected regression to the mean after an injury-marred preseason. However, sharp bettors disagreed with the market's tentative pricing of Kansas City.

Timeline of Key Movements:

Within the first two hours of the line being posted at Sharp Book A on Sunday evening (eight days before game time), two large wagers totaling approximately $120,000 were placed on KC -1.5. The book moved to KC -2 within 30 minutes. By Monday morning, Market Maker B had also moved to KC -2, confirming the sharp signal.

Over the next three days, a pattern emerged: each time a retail book posted KC below -2.5, sharp money appeared on Kansas City within hours, nudging the line upward. By Wednesday, all four books had converged on KC -2.5. A second wave of sharp action on Thursday, coinciding with the release of a prominent power-rating model update, pushed the market to KC -3 at the sharp book and KC -2.5 at the retail books.

By Friday afternoon, the consensus had settled at KC -3 (-110) / BUF +3 (-110). Public money began flowing on Buffalo over the weekend --- 68% of bets were on the Bills --- but the line held firm at KC -3, suggesting the books were comfortable with their position.

CLV Analysis:

A bettor who placed KC -1.5 at the opening line achieved 1.5 points of positive CLV. In implied probability terms, this translates to approximately +3.5% CLV (the probability difference between covering a 1.5-point spread and a 3-point spread in the NFL is substantial due to key number dynamics). This is an exceptionally large CLV for a single NFL spread bet.

A bettor who waited until Wednesday and bet KC -2.5 still achieved +0.5 points of CLV, a modest but positive result. A bettor who bet on Saturday at KC -3 achieved zero CLV --- they paid the full closing price.

Result: Kansas City won 27-20, covering the -3 spread by exactly 4 points. Bettors who took KC at all price points won, but only those who bet early captured the CLV premium.

Game 2: Dallas at Cleveland --- Reverse Line Movement

Dallas opened as a 6-point road favorite, reflecting the market's assessment of a significant talent gap. However, this game illustrated a classic reverse line movement pattern.

Public money poured in on Dallas throughout the week. By Thursday, 78% of tickets and 65% of money were on Dallas -6. Under normal circumstances, this weight of public action would push the line higher. Instead, the line moved from -6 to -5.5 on Tuesday and then to -5 on Thursday, eventually closing at -4.5 on Sunday.

The explanation lay in the money composition. While the public backed Dallas in large numbers of small bets, several sharp accounts placed six-figure wagers on Cleveland +6 at multiple books on Monday and Tuesday. The books, recognizing the quality of these accounts, moved the line against the public. A second round of sharp action at +5 on Wednesday pushed the line further.

Sharp vs. Public Breakdown:

The average bet size on Cleveland was nearly double that of Dallas, and 14 of the 16 identified sharp tickets were on the Browns. The sportsbooks interpreted this as a clear sharp lean on Cleveland and moved the line accordingly, despite the overwhelming public preference for Dallas.

CLV Analysis:

A bettor who followed the sharp signal and bet Cleveland +6 at the open achieved 1.5 points of positive CLV when the line closed at +4.5. In implied probability, this is approximately +3.2% CLV. A bettor who waited and bet Cleveland +5 on Wednesday still achieved +0.5 points of CLV.

Result: Dallas won 24-21, a 3-point margin. Cleveland +6 covered comfortably. Cleveland +4.5 also covered. The sharp money was correct, and the line movement correctly reflected the superior information embedded in the sharp action.

Game 3: San Francisco at Philadelphia --- The Stable Market

Not every game produces dramatic line movement. SF -2.5 opened on Sunday and closed at SF -2.5 eight days later. The line barely flickered throughout the week, touching -3 briefly at one retail book on Wednesday before settling back.

This stability indicates strong market consensus. Neither sharp money nor public money created sufficient pressure to move the line in either direction. The bet percentages were relatively balanced: 54% on San Francisco, 46% on Philadelphia, with money percentages similarly split at 52%/48%.

What Stability Tells Us:

A stable line does not mean the market is uncertain --- it means the market's initial assessment was well-calibrated and subsequent information did not change the picture. For bettors, a stable line offers no CLV opportunity. There is no "right time" to bet because the price never changes. The line opened correctly and stayed there.

Result: San Francisco won 20-17, covering -2.5 by exactly half a point. The market was accurate in assessing this as a close game with a slight San Francisco edge.

Game 4: Miami at Los Angeles Chargers --- The Full Side Flip

This game featured the most dramatic line movement of the slate: a full side flip from MIA +1 to MIA -1. The Dolphins opened as 1-point underdogs but closed as 1-point favorites, a 2-point swing that crossed through the pivotal pick'em number.

The flip was driven by a combination of factors. On Monday, a report surfaced that the Chargers' top cornerback would miss the game with a hamstring injury. Sharp Book A moved from MIA +1 to pick'em within an hour. By Tuesday, a second report confirmed the starting right tackle was also doubtful. Market Maker B moved to MIA -0.5.

The decisive push came Wednesday when a respected power-rating model released its Week 1 numbers with Miami rated 2.5 points better than the Chargers on a neutral field. With a typical 1-point home-field adjustment for the Chargers, this implied a fair line of MIA -1.5. Sharp money flooded in, moving all four books to MIA -1 by Wednesday evening.

CLV Analysis:

This game offered the largest CLV opportunity of the week. A bettor who bet MIA +1 at the open achieved 2 points of positive CLV when the line closed at MIA -1. However, this CLV measurement is complicated by the fact that the line crossed through pick'em --- the bettor's +1 was not just 2 points better but crossed the zero threshold, which disproportionately affects win probability.

Result: Miami won 23-17, covering as both a 1-point underdog (original line) and a 1-point favorite (closing line). Early bettors profited handsomely.

Game 5: Denver at Seattle --- Public Money Dominant

This game illustrated a pure public-money move. Denver opened at +3, and steady public interest in Seattle (the home favorite with a popular quarterback) pushed the line to DEN +4.5 by close.

There was no identifiable sharp action on either side. The movement was driven entirely by the 73% of bets and 71% of money that landed on Seattle. The money percentage matched the ticket percentage, indicating that the bets were uniformly small recreational wagers without large sharp positions offsetting them.

Why This Matters for Market Efficiency:

Public-driven line moves are less informative than sharp-driven moves. Research suggests that when lines move purely on public money, the movement often overshoots the true value, creating contrarian value on the other side. In this case, a bettor who took Denver +4.5 at the close was getting 1.5 points better than the opening number, but only because the public had pushed the line, not because new information justified the move.

Result: Seattle won 20-17, a 3-point margin. Denver +4.5 covered. Denver +3 (the opening line) also covered, but a bettor at +3 had zero CLV, while a bettor at +4.5 had negative CLV if they bet Seattle. The contrarian side (Denver) was the correct bet at the close.

Game 6: New York Giants at Minnesota --- Key Number Resistance

The Giants opened at +7, the quintessential NFL key number. Despite moderate line pressure (61% of money on Minnesota), the line resisted moving off 7 for most of the week. It briefly touched +7.5 at one retail book but snapped back.

On Friday, a burst of sharp action on the Giants at +7 pushed the line to +6.5 at the sharp book. Retail books followed by Sunday morning, and the game closed at NYG +6.

Key Number Dynamics:

The line's resistance to moving off 7 illustrates key number stickiness. Because approximately 9% of NFL games are decided by exactly 7 points, the probability gap between +6.5 and +7.5 is larger than the gap between, say, +5.5 and +6.5. Books know that moving through 7 has outsized implications for their liability and do so only under significant pressure.

Result: Minnesota won 28-21, a 7-point margin. NYG +7 pushed (no action). NYG +6 lost. The key number proved decisive.

Synthesis and Lessons

Week 1 vs. Mid-Season Line Movement

Across the six games, the average absolute line movement from open to close was 1.25 points. Research on mid-season NFL lines typically shows average absolute movement of 0.6-0.8 points. This confirms our hypothesis: Week 1 lines are more volatile because the market starts from a position of greater uncertainty.

Sharp Action Timing

In all four games with identifiable sharp action (Games 1, 2, 4, and 6), the first sharp move occurred within 48 hours of the line being posted --- Monday or Tuesday for lines posted on Sunday. This is consistent with the observation that sharp bettors move early in the week, when the most value is available, while the public bets closer to game time.

CLV Availability

The average positive CLV available to a bettor who bet the sharp side at the opening line across the four sharp-action games was +1.5 points (ranging from +0.5 to +2.0 points). At mid-season, this figure is typically closer to +0.5-0.8 points. Week 1 offers larger CLV opportunities because the market's initial uncertainty leaves more room for correction.

The Python Analysis

The accompanying code (case-study-code.py) implements a full line-movement tracking and CLV analysis pipeline for these six games. It generates line movement charts, computes CLV at various entry points, and runs a calibration analysis comparing opening-line implied probabilities to game outcomes. The code demonstrates that even with only six games, the structure of the analysis is identical to what would be applied to a full 272-game NFL season.

Discussion Questions

1. If Week 1 lines offer more CLV than mid-season lines, should a bettor allocate a larger fraction of their annual bankroll to Week 1? What are the risks of this approach?

2. In Game 2, the sportsbook moved the line against 78% of the public bets. How does the sportsbook manage its liability in this situation? Is it accepting a position against the public?

3. Game 3 showed a perfectly stable line. Does this mean the market was "more efficient" for this game than for Games 1 or 4? Or could it mean something else?

4. In Game 6, the key number of 7 proved decisive in determining the outcome for different bettors. Design a decision framework for when it is worth "buying" a half-point to stay on the right side of a key number.

5. If you could bet only at the opening line or only at the closing line for the entire NFL season, which would you choose and why? Under what conditions might the opposite choice be correct?