luckadjusted

Week 1 2023 · September 7, 2023

Lions at Chiefs, Week 1 2023: who deserved to win?

The Lions stole one. They beat the Chiefs 21–20, but replayed with the way both teams actually played, the Chiefs win 9 of 10. Luck ran their way: drops alone were worth 6.1 points to the Lions.

The Lions won on an off day: they played far below what the matchup promised. In a fresh game against the Chiefs they would win 41% of the time; with this day’s form, 10%. The numbers

Before kickoff the Chiefs were 62% favorites. The biggest swing (Q3, 11:04 left): the Chiefs were stopped on 3rd & 6, worth 60 points of win probability to the Lions.

Final

Detroit Lions 21
Kansas City Chiefs 20

September 7, 2023 · GEHA Field at Arrowhead Stadium · Closing line: Chiefs −4

Luck index +90 Lions very lucky · −90 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. Lions win 1, Chiefs win 9.

  1. 1 DET 40 KC 33
  2. 2 DET 20 KC 23
  3. 3 DET 21 KC 26
  4. 4 DET 27 KC 34
  5. 5 DET 20 KC 30
  6. 6 DET 9 KC 23
  7. 7 DET 17 KC 34
  8. 8 DET 13 KC 33
  9. 9 DET 14 KC 39
  10. 10 DET 6 KC 40

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.

The Lions won on an off day

They played far below what the matchup promised. In a fresh game against the Chiefs they would win 41% of the time; with this day’s form, 10%.

30 points apart for the Lions: the gap is how differently this game went from what the two teams usually are.

UnitThis gameUsual levelBetter or worse than usual
Lions offenseEPA per play gained +0.10 +0.13 worse by 0.03
Lions defenseEPA per play allowed −0.01 +0.15 better by 0.16
Chiefs offenseEPA per play gained −0.01 +0.21 worse by 0.22
Chiefs defenseEPA per play allowed +0.10 +0.07 worse by 0.03

EPA (expected points added) per play on competitive snaps, turnovers left out because they are valued as luck. Usual level: the team’s earlier games this season plus half of last season, pulled toward the league average. One team’s defense and the other team’s offense are the same snaps, so one game can’t fully say whose day it was; it shows how far this one was from both teams’ norms.

How 4,000 replays ended

Lions win 10% of them, Chiefs 90%, counting the 2% still level after regulation as half each. The line is what actually happened: Lions by 1.

Show as a table
Final margin in the replaysShare of replays
Lions by 17+0.8%
Lions by 9–162.2%
Lions by 1–86.6%
Level after regulation1.6%
Chiefs by 1–817.5%
Chiefs by 9–1622.8%
Chiefs by 17+48.5%

Where the luck was

Take the luck out

The final margin was Lions by 1. Remove the luck, one kind at a time, and it becomes Chiefs by 3.4.

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, 35 yds made · 93% expected
  • H. Butker, 39 yds made · 89% 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 86%. 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 Lions were.
#WhenWhat happenedWin probability forNext drive
1 Q2 5:21 The Lions were stopped on 3rd & 103rd & 4th downs · 29% expectedThe Lions fumbled and the Chiefs recoveredFumble bounces · loose balls are close to 50/50 +16% KC DET: Punt
2 Q3 11:04 The Chiefs were stopped on 3rd & 63rd & 4th downs · 40% expectedThe Chiefs were intercepted on a well-placed throwInterceptions · 0% expected to stay out of the defense's handsReturn touchdown by the LionsSpecial teams +60% DET KC: Punt
3 Q4 5:51 The Chiefs were stopped on 3rd & 13rd & 4th downs · 76% expected +11% DET KC: Punt
4 Q4 2:33 The Lions were stopped on 4th & 23rd & 4th downs · 61% expected +24% KC DET: End of game
5 Q4 2:30 K. Toney dropped a catchable passDrops · 3 drops on 27 catchable balls before this +13% DET KC: Turnover on downs
6 Q4 2:25 Offensive Holding on the Chiefs, 10 yards, wiping out the playJudgment calls +28% DET DET: End of game
7 Q4 2:19 S. Moore dropped a catchable passDrops · 2 drops on 31 catchable balls before this +16% DET KC: Turnover on downs
8 Q4 2:09 The Chiefs were stopped on 4th & 253rd & 4th downs · 16% expectedFalse Start on the Chiefs, 5 yardsPre-snap flags +25% DET KC: End of game

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.

  • Travis Kelce (KC TE), out · 1.0 pts
  • Chris Jones (KC DT), out (IR) · 0.8 pts
  • Isaiah Buggs (DET DT), 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

Lions 39% · Chiefs 61%

Final margin
Lions by 1
Luck in points
4.4 for the Lions
Luck-adjusted margin
Chiefs by 3.4
Replay with same day's form
Lions 10% · Chiefs 90% 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; injuries from snap counts and injury reports.

Methodology and validation · All Week 1 2023 games · Lions · Chiefs

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