luckadjusted

Week 8 2021 · October 31, 2021

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

49ers at Bears, Week 8 2021: who deserved to win?

The 49ers beat the Bears 33–22, and it was no fluke: replayed with the way both teams actually played, the 49ers win 10 of 10. The Bears had the bounces: fumble bounces alone were worth 3.1 points to the Bears.

Before kickoff the 49ers were 63% favorites. The biggest swing (Q4, 9:43 left): the Bears converted 4th & 1, worth 29 points of win probability to the Bears.

Final

San Francisco 49ers 33
Chicago Bears 22

October 31, 2021 · Soldier Field · Closing line: 49ers −4.5

Luck index +4 49ers about even · −4 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. 49ers win 10, Bears win 0.

  1. 1 SF 44 CHI 10
  2. 2 SF 33 CHI 7
  3. 3 SF 26 CHI 3
  4. 4 SF 35 CHI 16
  5. 5 SF 31 CHI 14
  6. 6 SF 30 CHI 16
  7. 7 SF 27 CHI 16
  8. 8 SF 33 CHI 24
  9. 9 SF 19 CHI 14
  10. 10 SF 16 CHI 14

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

49ers win 96% of them, Bears 4%, counting the 1% still level after regulation as half each. The line is what actually happened: 49ers by 11.

Show as a table
Final margin in the replaysShare of replays
49ers by 17+63.7%
49ers by 9–1618.9%
49ers by 1–813.0%
Level after regulation0.7%
Bears by 1–83.0%
Bears by 9–160.7%
Bears by 17+0.1%

Where the luck was

Take the luck out

The final margin was 49ers by 11. Remove the luck, one kind at a time, and it becomes 49ers by 20.3.

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.

  • J. Slye, 48 yds missed · 71% expected
  • C. Santos, 39 yds made · 87% expected
  • J. Slye, 48 yds made · 71% expected
  • J. Slye, 52 yds made · 64% expected
  • C. Santos, 40 yds made · 85% expected
  • J. Slye, 22 yds made · 98% expected
  • C. Santos, 25 yds made · 98% expected
  • J. Slye, 32 yds made · 94% 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 84%. 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 49ers were.
#WhenWhat happenedWin probability forNext drive
1 Q1 14:45 The 49ers converted 3rd & 103rd & 4th downs · 27% expected +9% SF SF: Missed field goal
2 Q1 12:36 The 49ers converted 4th & 13rd & 4th downs · 73% expected +7% SF SF: Missed field goal
3 Q1 9:53 J. Slye missed 48-yard field goalKicks · 71% expected for him, 22 of 32 from 45+ before +8% CHI SF: Field goal
4 Q3 12:17 The Bears converted 3rd & 133rd & 4th downs · 20% expected +7% CHI CHI: Field goal
5 Q3 7:28 The 49ers converted 3rd & 193rd & 4th downs · 17% expected +23% SF SF: Touchdown
6 Q3 6:00 The 49ers converted 3rd & 23rd & 4th downs · 52% expected +8% SF SF: Touchdown
7 Q4 9:43 The Bears converted 4th & 13rd & 4th downs · 70% expected +29% CHI CHI: Touchdown
8 Q4 9:32 The Bears missed an extra pointKicks · extra points are made about 94% of the time +8% SF CHI: Punt

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.

  • Germain Ifedi (CHI T), out (IR) · 0.8 pts
  • Khalil Mack (CHI LB), out · 0.6 pts
  • David Montgomery (CHI RB), out (IR) · 0.4 pts
  • George Kittle (SF TE), out (IR) · 1.1 pts
  • Deommodore Lenoir (SF CB), out · 0.5 pts
  • Jaquiski Tartt (SF SS), out (IR) · 0.4 pts
  • Jason Verrett (SF CB), out (IR) · 0.4 pts
  • Richie James (SF WR), out (IR) · 0.4 pts
  • Robbie Gould (SF K), out (IR) · 0.3 pts
  • Tarvarius Moore (SF DB), out (IR) · 0.3 pts
  • Azeez Al-Shaair (SF LB), out · 0.3 pts
  • Javon Kinlaw (SF DT), out (IR) · 0.3 pts
  • Dre Greenlaw (SF LB), out (IR) · 0.2 pts
  • Justin Skule (SF OL), 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

49ers 100% · Bears 0%

Final margin
49ers by 11
Luck in points
9.3 for the Bears
Luck-adjusted margin
49ers by 20.3
Replay with same day's form
49ers 96% · Bears 4% 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 8 2021 games · 49ers · Bears

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