luckadjusted

Week 15 2024 · December 15, 2024

Bills at Lions, Week 15 2024: who deserved to win?

The Bills beat the Lions 48–42, and it was no fluke: replayed with the way both teams actually played, the Bills win 9 of 10.

An off day for the Lions: their defense played far below its usual level. In a fresh game against the Bills they would win 44% of the time; with this day’s form, 10%. The numbers

Before kickoff the Lions were 57% favorites. The biggest swing (Q2, 1:47 left): T. Bass missed 24-yard field goal, worth 10 points of win probability to the Lions.

Final

Buffalo Bills 48
Detroit Lions 42

December 15, 2024 · Ford Field · Closing line: Lions −2.5

Luck index +10 Bills about even · −10 Lions

Each team’s own plays from this game, resampled into new drives 4,000 times: with the way both teams actually played, how often does this performance win? How the replay works

Ten replays. Bills win 9, Lions win 1.

  1. 1 BUF 38 DET 3
  2. 2 BUF 52 DET 24
  3. 3 BUF 36 DET 13
  4. 4 BUF 37 DET 19
  5. 5 BUF 35 DET 20
  6. 6 BUF 27 DET 14
  7. 7 BUF 36 DET 27
  8. 8 BUF 27 DET 21
  9. 9 BUF 36 DET 33
  10. 10 BUF 27 DET 34

Three other ways to ask

Each answers a different question, so none of them replaces the replay above.

The closing betting line, turned into a probability. What everyone knew before the game.

The line plus what this game showed, weighted by how much one game can tell. It stays close to the line because one game says little.

Every kick, fumble bounce, drop, conversion and judgment call redrawn; everything else fixed. The narrowest view of luck.

An off day for the Lions

Their defense played far below its usual level. In a fresh game against the Bills they would win 44% of the time; with this day’s form, 10%.

34 points apart for the Lions: the gap is how differently this game went from what the two teams usually are.

UnitThis gameUsual levelBetter or worse than usual
Bills offenseEPA per play gained +0.56 +0.20 better by 0.37
Bills defenseEPA per play allowed +0.10 +0.12 better by 0.02
Lions offenseEPA per play gained +0.10 +0.18 worse by 0.08
Lions defenseEPA per play allowed +0.56 +0.07 worse by 0.49

EPA (expected points added) per play on competitive snaps, turnovers left out because they are valued as luck. Usual level: the team’s earlier games this season plus half of last season, pulled toward the league average. One team’s defense and the other team’s offense are the same snaps, so one game can’t fully say whose day it was; it shows how far this one was from both teams’ norms.

How 4,000 replays ended

Bills win 90% of them, Lions 10%, counting the 2% still level after regulation as half each. The line is what actually happened: Bills by 6.

Show as a table
Final margin in the replaysShare of replays
Bills by 17+52.2%
Bills by 9–1620.1%
Bills by 1–815.9%
Level after regulation2.2%
Lions by 1–86.5%
Lions by 9–162.1%
Lions by 17+1.0%

Where the luck was

What the luck was worth

Every lucky and unlucky play, weighted by the moment it happened: its swing in win probability, added up by kind. A missed kick in a decided game counts for nothing; the same kick at the end of a tie game can be most of a win.

Swings add up across a game, so in one that went back and forth they can pass 100%. On the scoreboard the same luck was worth +3.7 points to the Lions: the final margin was Bills by 6, without the luck Bills by 9.7. Luck shares are the fitted ones (how much of each kind is luck).

The kicks

How likely each kicker was to make that kick (his own record, the distance and the weather), and what happened.

  • T. Bass, 24 yds missed · 98% expected
  • J. Bates, 52 yds missed · 73% expected
  • T. Bass, 50 yds made · 73% expected
  • T. Bass, 41 yds made · 87% expected
Bar: expected chance of a make. Filled dot: made. Open dot: missed or blocked.

Penalties: Bills 6 for 49 yards, Lions 5 for 41 yards

Every accepted flag, in order, and what it did to the helped team’s chance of winning at that moment, including any play it wiped out (points on the scoreboard in grey). A flag in a decided game is worth nothing; one at the turn of a close game can be worth most of a win. Judgment calls count toward luck, pre-snap fouls mostly don’t. How calls are valued

WhenFlagWin probability for
Q2 13:36 Offensive Holding on the Bills, 10 yards +3% DET +1.2 pts
Q2 3:01 Roughing the Passer on the Lions (Kwon Alexander), 3 yards +1% BUF +0.7 pts
Q2 1:53 False Start on the Bills, 5 yards · pre-snap +1% DET +1.6 pts
Q2 0:36 Intentional Grounding on the Bills (Josh Allen), 11 yards +3% DET +0.9 pts
Q3 11:29 Offensive Holding on the Bills, 8 yards 0% DET +0.7 pts
Q3 5:17 Face Mask on the Lions, 15 yards +1% BUF +1.4 pts
Q3 3:43 Low Block on the Lions (Za'Darius Smith), 3 yards 0% BUF +0.5 pts
Q3 2:52 Offensive Holding on the Lions, 10 yards 0% BUF +0.8 pts
Q4 9:28 Offensive Holding on the Lions, 10 yards 0% BUF +1.1 pts
Q4 2:55 Offensive Holding on the Bills, 10 yards, wiping out the play +2% DET +4.3 pts
Q4 2:50 False Start on the Bills, 5 yards · pre-snap 0% DET +0.3 pts

Bills penalties, every game · Lions penalties, every game · All teams, 2024

When it happened

Lions’ chance of winning

As low as 0% and as high as 55%. Numbers mark the biggest luck moments, listed below.

nflfastR’s in-game win probability. It ignores the betting line, so it starts near even. Shaded above the middle while the Lions were ahead in it, below while the Bills were.
#WhenWhat happenedWin probability forNext drive
1 Q1 11:49 The Bills converted 3rd & 53rd & 4th downs · 46% expected +8% BUF BUF: Touchdown
2 Q2 13:45 The Lions converted 3rd & 93rd & 4th downs · 31% expected +7% DET DET: Touchdown
3 Q2 10:23 The Bills converted 4th & 23rd & 4th downs · 65% expected +8% BUF BUF: Touchdown
4 Q2 5:55 The Lions converted 4th & 43rd & 4th downs · 47% expected +7% DET DET: Touchdown
5 Q2 1:47 T. Bass missed 24-yard field goalKicks · 98% expected for him +10% DET BUF: End of half
6 Q2 0:46 The Lions were stopped on 3rd & 103rd & 4th downs · 30% expectedA. St. Brown dropped a catchable passDrops · 11 drops on 361 catchable balls before this +10% BUF DET: Missed field goal
7 Q2 0:42 J. Bates missed 52-yard field goalKicks · 73% expected for him, 7 of 8 from 45+ before +6% BUF DET: Punt
8 Q3 5:17 The Lions fumbled and the Bills recoveredFumble bounces · loose balls are close to 50/50Face Mask on the Lions, 15 yardsJudgment calls +4% BUF DET: Touchdown

Missing players

Key players (usually on the field for half the snaps or more) who missed this game or part of it, valued by position and quality. The same players are missing in every replay, so this counts as luck in points only.

  • Alex Anzalone (DET LB), out (IR) · 0.3 pts
  • Malcolm Rodriguez (DET LB), out (IR) · 0.2 pts
  • Rasul Douglas (BUF CB), out · 0.7 pts
  • Taylor Rapp (BUF SS), out · 0.5 pts
  • Damar Hamlin (BUF SS), out · 0.3 pts

Adjust the assumptions

Disagree with how much of a fumble bounce or a pass interference call is luck? Change it and the coin-flip replay reruns in your browser.

Only coin-flips re-rolled

Bills 87% · Lions 13%

Final margin
Bills by 6
Luck in points
3.7 for the Lions
Luck-adjusted margin
Bills by 9.7
Replay with same day's form
Bills 90% · Lions 10% unchanged: why
How much of each is luck?

0% treats it as skill, 100% as pure luck. The tick is our fit.

What counts

We tested momentum on 19,000 lucky breaks and found none, so it's off by default. Why

Flip a play

Force the other outcome, in this game and in every replay: a made kick becomes a miss, a stop becomes a conversion, a flag goes the other way.

About these numbers

Play-by-play and win probability from nflfastR via nflverse; kicks valued against each kicker’s own record; drops and interception-worthy throws from FTN charting; injuries from snap counts and injury reports.

Methodology and validation · All Week 15 2024 games · Bills · Lions

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