luckadjusted

Week 5 2021 · October 10, 2021

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

Bills at Chiefs, Week 5 2021: who deserved to win?

The Bills beat the Chiefs 38–20, but it was a coin flip: replayed with the way both teams played, the Bills win 4 of 10. Luck ran their way: fumble bounces alone were worth 3.1 points to the Bills.

Before kickoff the Chiefs were 57% favorites. The biggest swing (Q3, 7:20 left): the Chiefs were stopped on 3rd & 5, worth 18 points of win probability to the Bills.

Final

Buffalo Bills 38
Kansas City Chiefs 20

October 10, 2021 · GEHA Field at Arrowhead Stadium · Closing line: Chiefs −2.5

Luck index +57 Bills lucky · −57 Chiefs

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 4, Chiefs win 6.

  1. 1 BUF 44 KC 24
  2. 2 BUF 34 KC 24
  3. 3 BUF 23 KC 17
  4. 4 BUF 33 KC 30
  5. 5 BUF 31 KC 33
  6. 6 BUF 16 KC 21
  7. 7 BUF 20 KC 29
  8. 8 BUF 13 KC 26
  9. 9 BUF 23 KC 41
  10. 10 BUF 23 KC 49

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 43% of them, Chiefs 57%, counting the 3% still level after regulation as half each. The line is what actually happened: Bills by 18.

Show as a table
Final margin in the replaysShare of replays
Bills by 17+8.6%
Bills by 9–1612.8%
Bills by 1–819.8%
Level after regulation2.6%
Chiefs by 1–824.4%
Chiefs by 9–1616.5%
Chiefs by 17+15.4%

Where the luck was

Take the luck out

The final margin was Bills by 18. Remove the luck, one kind at a time, and it becomes Bills 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.

  • H. Butker, 38 yds made · 92% expected
  • T. Bass, 30 yds made · 96% expected
  • H. Butker, 54 yds made · 71% expected
Bar: expected chance of a make. Filled dot: made. Open dot: missed or blocked.

When it happened

Chiefs’ chance of winning

As low as 0% and as high as 85%. 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 12:12 Defensive Offside on the Bills (A.J. Epenesa), 4 yardsPre-snap flags · 2 flags in 602 snaps before, position avg 1 per 266 +7% KC KC: Field goal
2 Q1 7:33 The Bills converted 3rd & 23rd & 4th downs · 65% expected +8% BUF BUF: Touchdown
3 Q1 3:21 The Bills were stopped on 3rd & 113rd & 4th downs · 30% expectedIntentional Grounding on the Bills (Josh Allen), 18 yardsJudgment calls · 6 flags in 2577 snaps before, position avg 1 per 711 +9% KC BUF: Punt
4 Q1 3:14 Defensive Offside on the Chiefs, 5 yards, wiping out the playPre-snap flags +8% KC BUF: Punt
5 Q2 4:56 The Bills converted 3rd & 83rd & 4th downs · 36% expected +14% BUF BUF: Field goal
6 Q2 0:31 Offensive Pass Interference on the Chiefs, 10 yards, wiping out the playJudgment calls +7% BUF BUF: End of half
7 Q3 7:20 The Chiefs were stopped on 3rd & 53rd & 4th downs · 43% expectedReturn touchdown by the BillsSpecial teams +18% BUF KC: Turnover
8 Q4 11:50 Roughing the Passer on the Chiefs (Frank Clark), 15 yards, wiping out the playJudgment calls · 9 flags in 1857 snaps before, position avg 1 per 266 +16% BUF BUF: 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.

  • Chris Jones (KC DT), out · 0.8 pts
  • Charvarius Ward (KC CB), out · 0.6 pts
  • Matt Milano (BUF LB), out · 0.6 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 99% · Chiefs 1%

Final margin
Bills by 18
Luck in points
2.3 for the Chiefs
Luck-adjusted margin
Bills by 20.3
Replay with same day's form
Bills 43% · Chiefs 57% 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 5 2021 games · Bills · Chiefs

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