luckadjusted
NFL Week 9 · 2026

Week 18 2021 · January 8, 2022

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

Chiefs at Broncos, Week 18 2021: who deserved to win?

The Chiefs beat the Broncos 28–24, and the replays back it up: with the way both teams actually played, the Chiefs win 8 of 10.

Before kickoff the Chiefs were 80% favorites. The game turned on a luck play (Q4, 7:57 left): Return touchdown by the Chiefs, worth 93 points of win probability to the Chiefs.

Final

Kansas City Chiefs 28
Denver Broncos 24

January 8, 2022 · Empower Field at Mile High · Closing line: Chiefs −11.5

Luck index +20 Chiefs about even · −20 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. Chiefs win 8, Broncos win 2.

  1. 1 KC 49 DEN 24
  2. 2 KC 24 DEN 6
  3. 3 KC 31 DEN 17
  4. 4 KC 26 DEN 13
  5. 5 KC 34 DEN 24
  6. 6 KC 28 DEN 21
  7. 7 KC 17 DEN 13
  8. 8 KC 31 DEN 28
  9. 9 KC 14 DEN 17
  10. 10 KC 20 DEN 31

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

Chiefs win 80% of them, Broncos 20%, counting the 5% still level after regulation as half each. The line is what actually happened: Chiefs by 4.

Show as a table
Final margin in the replaysShare of replays
Chiefs by 17+23.4%
Chiefs by 9–1623.0%
Chiefs by 1–829.8%
Level after regulation4.7%
Broncos by 1–813.0%
Broncos by 9–164.5%
Broncos by 17+1.6%

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 +6.8 points to the Chiefs: the final margin was Chiefs by 4, without the luck Broncos by 2.9. Luck shares are the fitted ones (how much of each kind 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, 34 yds made · 95% expected
  • H. Butker, 51 yds made · 74% expected
  • B. McManus, 31 yds made · 97% expected
Bar: expected chance of a make. Filled dot: made. Open dot: missed or blocked.

Penalties: Chiefs 5 for 45 yards, Broncos 6 for 45 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 10:07 Encroachment on the Broncos (Shelby Harris), 5 yards · pre-snap +6% KC +0.6 pts
Q1 5:22 Roughing the Kicker on the Chiefs, 15 yards +7% DEN +3.7 pts
Q2 14:20 Roughing the Passer on the Broncos (Bradley Chubb), 15 yards +5% KC +1.2 pts
Q2 5:16 Illegal Use of Hands on the Broncos (Dre'Mont Jones), 5 yards +2% KC +0.8 pts
Q2 3:09 Defensive Pass Interference on the Broncos (Kyle Fuller), 10 yards +5% KC +1.4 pts
Q2 3:00 Offensive Holding on the Chiefs, 10 yards +5% DEN +1.6 pts
Q3 5:38 False Start on the Broncos (Albert Okwuegbunam), 5 yards · pre-snap +1% KC +0.6 pts
Q3 4:17 Illegal Forward Pass on the Chiefs (Patrick Mahomes), 5 yards +2% DEN +0.5 pts
Q3 3:54 Offensive Holding on the Chiefs, 10 yards, wiping out the play +6% DEN +1.8 pts
Q4 11:11 False Start on the Broncos, 5 yards · pre-snap +2% KC +0.5 pts
Q4 2:03 False Start on the Chiefs, 5 yards · pre-snap 0% DEN +0.8 pts

Chiefs penalties, every game · Broncos penalties, every game · All teams, 2021

When it happened

Broncos’ 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 Broncos were ahead in it, below while the Chiefs were.
#WhenWhat happenedWin probability forNext drive
1 Q1 5:22 Roughing the Kicker on the Chiefs, 15 yardsJudgment calls +7% DEN DEN: Touchdown
2 Q3 10:52 The Chiefs converted 3rd & 73rd & 4th downs · 40% expected +7% KC KC: Touchdown
3 Q3 10:01 The Broncos converted 3rd & 133rd & 4th downs · 23% expected +9% DEN DEN: Touchdown
4 Q3 3:54 Offensive Holding on the Chiefs, 10 yards, wiping out the playJudgment calls +6% DEN DEN: Opp touchdown
5 Q4 14:54 The Chiefs were stopped on 3rd & 63rd & 4th downs · 43% expected +7% DEN KC: Field goal
6 Q4 7:57 The game turned hereThe Broncos fumbled and the Chiefs recoveredFumble bounces · loose balls are close to 50/50Return touchdown by the ChiefsSpecial teams +93% KC DEN: Field goal
7 Q4 6:06 The Broncos converted 3rd & 63rd & 4th downs · 37% expected +12% DEN DEN: Field goal
8 Q4 4:45 The Broncos were stopped on 3rd & 93rd & 4th downs · 29% expected +6% KC DEN: Field goal

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.

  • Teddy Bridgewater (DEN QB), out (IR), replaced by d.lock · 4.6 pts
  • Bobby Massie (DEN T), out · 0.8 pts
  • Ronald Darby (DEN CB), out (IR) · 0.7 pts
  • Calvin Anderson (DEN T), out (IR) · 0.6 pts
  • Kareem Jackson (DEN SS), out (IR) · 0.5 pts
  • Dalton Risner (DEN G), out (IR) · 0.3 pts
  • Kenny Young (DEN LB), 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

Chiefs 75% · Broncos 25%

Final margin
Chiefs by 4
Luck in points
6.8 for the Chiefs
Luck-adjusted margin
Broncos by 2.8
Replay with same day's form
Chiefs 80% · Broncos 20% 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 18 2021 games · Chiefs · Broncos

More from Week 18 2021