luckadjusted

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 were the better team on the day: replayed with the same form, they win 7 of 10. The Lions had the bounces: judgment calls alone were worth 5.3 points to the Lions.

Before kickoff the Bears were 59% favorites. The biggest swing (Q2, 3:09 left): the Lions were stopped on 3rd & 3, worth 12 points of win probability to the Bears.

Final

Detroit Lions 14
Chicago Bears 24

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

Luck index +28 Bears lucky · −28 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 20 CHI 3
  2. 2 DET 16 CHI 9
  3. 3 DET 13 CHI 10
  4. 4 DET 29 CHI 31
  5. 5 DET 5 CHI 10
  6. 6 DET 10 CHI 19
  7. 7 DET 14 CHI 26
  8. 8 DET 10 CHI 26
  9. 9 DET 14 CHI 34
  10. 10 DET 6 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 28% of them, Bears 72%, 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+3.0%
Lions by 9–168.3%
Lions by 1–815.4%
Level after regulation4.1%
Bears by 1–824.1%
Bears by 9–1621.9%
Bears by 17+23.1%

Where the luck was

Take the luck out

The final margin was Bears by 10. Remove the luck, one kind at a time, and it becomes Bears by 13.2.

Each row takes one kind of luck out of the margin. Color shows which team it helped. Luck shares are the fitted ones (how much of each component is luck).

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 · 73% expected +7% 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 Q2 11:42 The Lions converted 3rd & 23rd & 4th downs · 60% expected +5% DET DET: Turnover on downs
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 3:09 The Lions were stopped on 3rd & 33rd & 4th downs · 44% expectedThe 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 +12% CHI DET: Punt
6 Q2 1:09 The Bears were stopped on 3rd & 23rd & 4th downs · 61% expected +5% DET CHI: End of half
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 · 66% 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 1% · Bears 99%

Final margin
Bears by 10
Luck in points
3.2 for the Lions
Luck-adjusted margin
Bears by 13.2
Replay with same day's form
Lions 28% · Bears 72% 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 (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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