luckadjusted
NFL Week 9 · 2026

Week 4 2021 · October 3, 2021

No FTN charting for this game (drops and interception-worthy throws are not modelled).

Lions at Bears, Week 4 2021: who deserved to win?

The Bears beat the Lions 24–14, and the replays lean their way: with the same day's form, they win 7 of 10.

Before kickoff the Bears were 59% favorites.

Final

Detroit Lions 14
Chicago Bears 24

October 3, 2021 · Soldier Field · Closing line: Bears −3

Luck index +27 Bears lucky · −27 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. Lions win 3, Bears win 7.

  1. 1 DET 24 CHI 6
  2. 2 DET 27 CHI 19
  3. 3 DET 16 CHI 13
  4. 4 DET 30 CHI 32
  5. 5 DET 24 CHI 28
  6. 6 DET 16 CHI 24
  7. 7 DET 13 CHI 24
  8. 8 DET 10 CHI 24
  9. 9 DET 20 CHI 37
  10. 10 DET 7 CHI 33

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.

How 4,000 replays ended

Lions win 27% of them, Bears 73%, counting the 4% still level after regulation as half each. The line is what actually happened: Bears by 10.

Show as a table
Final margin in the replaysShare of replays
Lions by 17+3.9%
Lions by 9–167.6%
Lions by 1–814.5%
Level after regulation4.1%
Bears by 1–824.9%
Bears by 9–1621.2%
Bears by 17+23.8%

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 +1.4 points to the Bears: the final margin was Bears by 10, without the luck Bears by 8.6. Luck shares are the fitted ones (how much of each kind is luck).

Penalties: Lions 4 for 26 yards, Bears 7 for 61 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 half toward luck; pre-snap fouls, which repeat, don’t count. How calls are valued

WhenFlagWin probability for
Q1 2:57 Unnecessary Roughness on the Bears (Khyiris Tonga), 8 yards +2% DET +1.0 pts
Q2 13:43 Defensive Pass Interference on the Bears (Roquan Smith), 10 yards +3% DET +1.3 pts
Q2 9:35 False Start on the Bears, 3 yards · pre-snap +1% DET +0.8 pts
Q2 6:06 Roughing the Passer on the Bears (Khalil Mack), 15 yards +6% DET +2.0 pts
Q2 3:09 Illegal Forward Pass on the Bears (Khalil Mack), 5 yards +1% DET +0.5 pts
Q2 0:50 False Start on the Lions, 5 yards · pre-snap +2% CHI +0.3 pts
Q3 9:59 Offensive Pass Interference on the Lions (Amon-Ra St. Brown), 10 yards +1% CHI +0.9 pts
Q3 6:49 Kick Catch Interference on the Bears (Xavier Crawford), 15 yards +1% DET +1.3 pts
Q4 6:48 Defensive Offside on the Bears (Jeremiah Attaochu), 5 yards · pre-snap 0% DET +0.6 pts
Q4 2:36 Defensive Pass Interference on the Lions (Amani Oruwariye), 6 yards, wiping out the play 0% DET +0.4 pts
Q4 1:07 Defensive Offside on the Lions, 5 yards, wiping out the play · pre-snap 0% DET +0.6 pts

Lions penalties, every game · Bears penalties, every game · All teams, 2021

When it happened

Bears’ chance of winning

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 Bears were ahead in it, below while the Lions were.
#WhenWhat happenedWin probability forNext drive
1 Q1 12:18 The Bears converted 4th & 13rd & 4th downs · 76% expected +4% CHI CHI: Touchdown
2 Q1 2:48 The Lions fumbled and the Bears recoveredFumble bounces · loose balls are close to 50/50 +6% CHI DET: Turnover on downs
3 Q1 0:29 The Bears converted 3rd & 43rd & 4th downs · 48% expected +4% CHI CHI: Touchdown
4 Q2 6:06 Roughing the Passer on the Bears (Khalil Mack), 15 yardsJudgment calls · 4 flags in 2053 snaps before, position avg 1 per 409 +6% DET DET: Turnover
5 Q2 5:21 The Lions converted 3rd & 113rd & 4th downs · 27% expected +5% DET DET: Turnover
6 Q2 3:09 The Lions fumbled and the Bears recoveredFumble bounces · loose balls are close to 50/50Illegal Forward Pass on the Bears (Khalil Mack), 5 yardsJudgment calls · 4 flags in 2053 snaps before, position avg 1 per 409 +4% CHI DET: Punt
7 Q4 6:42 The Lions fumbled and recovered it themselvesFumble bounces · loose balls are close to 50/50 +7% DET DET: Turnover on downs
8 Q4 4:19 The Lions were stopped on 4th & 13rd & 4th downs · 68% expected +7% CHI –

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.

  • Andy Dalton (CHI QB), out, replaced by j.fields · 2.2 pts
  • Tashaun Gipson (CHI DB), out · 0.5 pts
  • Tashaun Gipson (CHI FS), out · 0.4 pts
  • Danny Trevathan (CHI LB), out (IR) · 0.3 pts
  • Taylor Decker (DET T), out (IR) · 1.1 pts
  • Trey Flowers (DET LB), out · 0.3 pts
  • Kevin Strong (DET DT), out (IR) · 0.2 pts
  • Austin Seibert (DET K), out (IR) · 0.2 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

Lions 7% · Bears 93%

Final margin
Bears by 10
Luck in points
1.4 for the Bears
Luck-adjusted margin
Bears by 8.6
Replay with same day's form
Lions 27% · Bears 73% unchanged: why
How much of each is luck?

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

What counts

None by default: our tests measured no carryover after a lucky break. Slide it up to count a break for more than its own swing. 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 (not available for this game); injuries from snap counts and injury reports. No FTN charting for this game (drops and interception-worthy throws are not modelled).

Methodology and validation · All Week 4 2021 games · Lions · Bears

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