luckadjusted

AFC Championship 2020 · January 24, 2021

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

Bills at Chiefs, AFC Championship 2020: who deserved to win?

The Chiefs beat the Bills 38–24, and it was no fluke: replayed with the way both teams actually played, the Chiefs win 9 of 10.

Before kickoff the Chiefs were 59% favorites. The biggest swing (Q2, 12:42 left): the Bills were stopped on 3rd & 7, worth 14 points of win probability to the Chiefs.

Final

Buffalo Bills 24
Kansas City Chiefs 38

January 24, 2021 · Arrowhead Stadium · Closing line: Chiefs −3

Luck index +15 Chiefs about even · −15 Bills

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. Bills win 2, Chiefs win 8.

  1. 1 BUF 28 KC 16
  2. 2 BUF 13 KC 10
  3. 3 BUF 38 KC 40
  4. 4 BUF 23 KC 28
  5. 5 BUF 26 KC 33
  6. 6 BUF 24 KC 34
  7. 7 BUF 35 KC 48
  8. 8 BUF 32 KC 49
  9. 9 BUF 17 KC 38
  10. 10 BUF 17 KC 48

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

Bills win 15% of them, Chiefs 85%, counting the 2% still level after regulation as half each. The line is what actually happened: Chiefs by 14.

Show as a table
Final margin in the replaysShare of replays
Bills by 17+1.2%
Bills by 9–163.2%
Bills by 1–89.0%
Level after regulation1.9%
Chiefs by 1–820.7%
Chiefs by 9–1625.1%
Chiefs by 17+38.8%

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 +1.4 points to the Bills: the final margin was Chiefs by 14, without the luck Chiefs by 15.4. 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.

  • T. Bass, 51 yds made · 70% expected
  • T. Bass, 20 yds made · 99% expected
  • H. Butker, 45 yds made · 82% expected
  • T. Bass, 27 yds made · 97% expected
  • T. Bass, 51 yds made · 70% expected
  • Extra point missed · 93% expected
Bar: expected chance of a make. Filled dot: made. Open dot: missed or blocked.

Penalties: Bills 4 for 38 yards, Chiefs 3 for 32 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 toward luck, pre-snap fouls mostly don’t. How calls are valued

WhenFlagWin probability for
Q2 13:45 Unnecessary Roughness on the Chiefs (Bashaud Breeland), 15 yards +6% BUF +1.4 pts
Q2 12:42 Intentional Grounding on the Bills (Josh Allen), 16 yards +5% KC +1.2 pts
Q3 8:19 False Start on the Bills, 5 yards · pre-snap +2% KC +0.8 pts
Q3 7:31 Defensive Holding on the Chiefs (L'Jarius Sneed), 5 yards +1% BUF +1.3 pts
Q3 3:39 Defensive Holding on the Bills (Tre'Davious White), 2 yards 0% KC +0.6 pts
Q4 4:32 Roughing the Passer on the Chiefs (Alex Okafor), 12 yards 0% BUF +1.6 pts
Q4 3:07 Unnecessary Roughness on the Bills (Quinton Jefferson), 15 yards 0% KC +1.9 pts

Bills penalties, every game · Chiefs penalties, every game · All teams, 2020

When it happened

Chiefs’ chance of winning

As low as 29% and as high as 100%. 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 Bills were.
#WhenWhat happenedWin probability forNext drive
1 Q1 12:44 The Bills converted 4th & 13rd & 4th downs · 74% expected +9% BUF BUF: Field goal
2 Q1 11:38 The Bills were stopped on 3rd & 33rd & 4th downs · 52% expected +5% KC BUF: Field goal
3 Q1 9:13 The Bills converted 3rd & 33rd & 4th downs · 52% expected +5% BUF BUF: Punt
4 Q1 6:30 The Chiefs fumbled and the Bills recoveredFumble bounces · loose balls are close to 50/50 +9% BUF KC: Touchdown
5 Q1 1:08 The Chiefs converted 4th & 13rd & 4th downs · 78% expected +6% KC KC: Touchdown
6 Q2 13:45 Unnecessary Roughness on the Chiefs (Bashaud Breeland), 15 yardsJudgment calls · 16 flags in 1856 snaps before, position avg 1 per 207 +6% BUF BUF: Punt
7 Q2 12:42 The Bills were stopped on 3rd & 73rd & 4th downs · 35% expectedIntentional Grounding on the Bills (Josh Allen), 16 yardsJudgment calls · 5 flags in 2223 snaps before, position avg 1 per 669 +14% KC BUF: Punt
8 Q3 5:56 The Bills were stopped on 3rd & 33rd & 4th downs · 44% expected +5% KC BUF: 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.

  • Sammy Watkins (KC WR), out · 0.7 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

Bills 0% · Chiefs 100%

Final margin
Chiefs by 14
Luck in points
1.4 for the Bills
Luck-adjusted margin
Chiefs by 15.4
Replay with same day's form
Bills 15% · Chiefs 85% 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 Conference championships 2020 games · Bills · Chiefs

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