luckadjusted

Week 13 2021 · December 5, 2021

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

Broncos at Chiefs, Week 13 2021: who deserved to win?

The Chiefs beat the Broncos 22–9 and were the better team on the day: replayed with the same form, they win 7 of 10. The Broncos had the bounces: judgment calls alone were worth 2.1 points to the Broncos.

Before kickoff the Chiefs were 74% favorites. The biggest swing (Q2, 1:12 left): the Broncos were stopped on 4th & 2, worth 8 points of win probability to the Chiefs.

Final

Denver Broncos 9
Kansas City Chiefs 22

December 5, 2021 · GEHA Field at Arrowhead Stadium · Closing line: Chiefs −8.5

Luck index +35 Chiefs lucky · −35 Broncos

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. Broncos win 3, Chiefs win 7.

  1. 1 DEN 30 KC 14
  2. 2 DEN 30 KC 21
  3. 3 DEN 20 KC 17
  4. 4 DEN 17 KC 20
  5. 5 DEN 20 KC 26
  6. 6 DEN 20 KC 27
  7. 7 DEN 20 KC 30
  8. 8 DEN 24 KC 37
  9. 9 DEN 17 KC 35
  10. 10 DEN 3 KC 28

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

Broncos win 35% of them, Chiefs 65%, counting the 2% still level after regulation as half each. The line is what actually happened: Chiefs by 13.

Show as a table
Final margin in the replaysShare of replays
Broncos by 17+5.1%
Broncos by 9–169.2%
Broncos by 1–819.5%
Level after regulation2.3%
Chiefs by 1–826.2%
Chiefs by 9–1620.8%
Chiefs by 17+17.1%

Where the luck was

Take the luck out

The final margin was Chiefs by 13. Remove the luck, one kind at a time, and it becomes Chiefs by 11.2.

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).

The kicks

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

  • H. Butker, 56 yds made · 54% expected
  • B. McManus, 42 yds made · 79% expected
  • H. Butker, 45 yds made · 76% expected
  • H. Butker, 26 yds made · 98% expected
  • Extra point missed · 93% expected
Bar: expected chance of a make. Filled dot: made. Open dot: missed or blocked.

When it happened

Chiefs’ 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 Chiefs were ahead in it, below while the Broncos were.
#WhenWhat happenedWin probability forNext drive
1 Q1 13:44 The Broncos were stopped on 3rd & 23rd & 4th downs · 60% expected +7% KC DEN: Punt
2 Q1 4:25 The Chiefs converted 3rd & 103rd & 4th downs · 31% expected +5% KC KC: Field goal
3 Q2 6:28 The Broncos converted 4th & 13rd & 4th downs · 73% expected +5% DEN DEN: Turnover on downs
4 Q2 4:27 The Broncos converted 4th & 73rd & 4th downs · 33% expected +8% DEN DEN: Turnover on downs
5 Q2 1:20 The Broncos were stopped on 3rd & 23rd & 4th downs · 52% expected +5% KC DEN: Turnover on downs
6 Q2 1:12 The Broncos were stopped on 4th & 23rd & 4th downs · 52% expected +8% KC DEN: End of half
7 Q3 10:22 The Broncos fumbled and recovered it themselvesFumble bounces · loose balls are close to 50/50 +5% DEN DEN: Punt
8 Q4 9:56 The Broncos were stopped on 4th & 23rd & 4th downs · 60% expectedReturn touchdown by the ChiefsSpecial teams +8% KC DEN: 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.

  • Mike Remmers (KC T), out (IR) · 0.6 pts
  • Rashad Fenton (KC CB), out · 0.3 pts
  • Lucas Niang (KC T), out · 0.2 pts
  • Graham Glasgow (DEN G), out (IR) · 0.4 pts
  • Bryce Callahan (DEN CB), out (IR) · 0.4 pts
  • Melvin Gordon (DEN RB), out · 0.3 pts
  • Mike Purcell (DEN NT), 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

Broncos 1% · Chiefs 99%

Final margin
Chiefs by 13
Luck in points
1.8 for the Chiefs
Luck-adjusted margin
Chiefs by 11.2
Replay with same day's form
Broncos 35% · Chiefs 65% 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 2021 games · Broncos · Chiefs

More from Week 13 2021