luckadjusted

Week 13 2020 · December 6, 2020

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

Lions at Bears, Week 13 2020: who deserved to win?

The Lions beat the Bears 34–30, and it was no fluke: replayed with the way both teams actually played, the Lions win 9 of 10. The Bears had the bounces: injuries alone were worth 2.3 points to the Bears.

An off day for the Bears: their defense played far below its usual level. In a fresh game against the Lions they would win 59% of the time; with this day’s form, 12%. The numbers

Before kickoff the Bears were 59% favorites. The biggest swing (Q4, 1:54 left): the Bears were stopped on 3rd & 4, worth 69 points of win probability to the Lions.

Final

Detroit Lions 34
Chicago Bears 30

December 6, 2020 · Soldier Field · Closing line: Bears −3

Luck index +12 Lions about even · −12 Bears

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 9, Bears win 1.

  1. 1 DET 48 CHI 16
  2. 2 DET 36 CHI 10
  3. 3 DET 29 CHI 9
  4. 4 DET 44 CHI 27
  5. 5 DET 44 CHI 30
  6. 6 DET 38 CHI 27
  7. 7 DET 29 CHI 21
  8. 8 DET 24 CHI 20
  9. 9 DET 23 CHI 21
  10. 10 DET 17 CHI 23

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 Bears

Their defense played far below its usual level. In a fresh game against the Lions they would win 59% of the time; with this day’s form, 12%.

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

UnitThis gameUsual levelBetter or worse than usual
Lions offenseEPA per play gained +0.32 +0.09 better by 0.23
Lions defenseEPA per play allowed +0.25 +0.17 worse by 0.08
Bears offenseEPA per play gained +0.25 +0.01 better by 0.24
Bears defenseEPA per play allowed +0.32 +0.06 worse by 0.26

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

Lions win 88% of them, Bears 12%, counting the 2% still level after regulation as half each. The line is what actually happened: Lions by 4.

Show as a table
Final margin in the replaysShare of replays
Lions by 17+49.3%
Lions by 9–1620.5%
Lions by 1–818.1%
Level after regulation2.1%
Bears by 1–86.6%
Bears by 9–162.6%
Bears by 17+0.8%

Where the luck was

Take the luck out

The final margin was Lions by 4. Remove the luck, one kind at a time, and it becomes Lions by 0.3.

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).

The kicks

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

  • C. Santos, 45 yds made · 75% expected
  • Extra point missed · 93% expected
  • Extra point missed · 93% expected
Bar: expected chance of a make. Filled dot: made. Open dot: missed or blocked.

When it happened

Bears’ chance of winning

As low as 0% and as high as 97%. 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 9:35 The Lions were stopped on 4th & 13rd & 4th downs · 75% expected +12% CHI DET: Touchdown
2 Q1 0:19 The Lions converted 3rd & 33rd & 4th downs · 45% expected +8% DET DET: Touchdown
3 Q2 15:00 The Bears converted 3rd & 63rd & 4th downs · 38% expected +7% CHI CHI: Touchdown
4 Q4 14:16 The Bears converted 3rd & 73rd & 4th downs · 35% expected +7% CHI CHI: Touchdown
5 Q4 1:54 The Bears were stopped on 3rd & 43rd & 4th downs · 47% expectedThe Bears fumbled and the Lions recoveredFumble bounces · loose balls are close to 50/50 +69% DET CHI: Turnover on downs
6 Q4 1:37 Horse Collar Tackle on the Lions (Jayron Kearse), 15 yardsJudgment calls · 3 flags in 905 snaps before, position avg 1 per 510 +14% CHI CHI: Turnover on downs
7 Q4 0:22 The Bears were stopped on 3rd & 53rd & 4th downs · 42% expected +8% DET CHI: Turnover on downs
8 Q4 0:16 The Bears were stopped on 4th & 13rd & 4th downs · 74% expected +29% DET –

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.

  • Bobby Massie (CHI OL), out (IR) · 0.5 pts
  • James Daniels (CHI OL), out (IR) · 0.3 pts
  • Desmond Trufant (DET CB), out (IR) · 0.8 pts
  • Kenny Golladay (DET WR), out · 0.7 pts
  • Trey Flowers (DET DE), out (IR) · 0.5 pts
  • Halapoulivaati Vaitai (DET T), out (IR) · 0.4 pts
  • Danny Shelton (DET DT), out (IR) · 0.3 pts
  • Jeff Okudah (DET CB), out · 0.2 pts
  • Da'Shawn Hand (DET DL), out · 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 38% · Bears 62%

Final margin
Lions by 4
Luck in points
3.7 for the Lions
Luck-adjusted margin
Lions by 0.3
Replay with same day's form
Lions 88% · Bears 12% 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 13 2020 games · Lions · Bears

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