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 36 points of win probability 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 game turned on a luck play (Q4, 2:25 left): Offensive Holding on the Chiefs, 10 yards, wiping out the play, worth 28 points of win probability to the Lions. The biggest single swing (Q3, 11:04 left): the Chiefs were stopped on 3rd & 6.

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 20 KC 13
  2. 2 DET 10 KC 13
  3. 3 DET 27 KC 32
  4. 4 DET 23 KC 30
  5. 5 DET 23 KC 33
  6. 6 DET 23 KC 37
  7. 7 DET 13 KC 30
  8. 8 DET 19 KC 39
  9. 9 DET 13 KC 38
  10. 10 DET 3 KC 37

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

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 +4.4 points to the Lions: the final margin was Lions by 1, without the luck Chiefs by 3.4. 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.

  • 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.

Penalties: Lions 4 for 63 yards, Chiefs 3 for 25 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 1:13 Offensive Holding on the Chiefs, 10 yards, wiping out the play +4% DET +1.1 pts
Q3 3:07 Defensive Pass Interference on the Lions (Cameron Sutton), 41 yards +9% KC +3.2 pts
Q3 2:06 Tripping on the Lions (David Montgomery), 12 yards +3% KC +2.0 pts
Q4 10:46 Delay of Game on the Lions, 5 yards · pre-snap +3% KC +0.8 pts
Q4 5:07 False Start on the Lions, 5 yards · pre-snap +4% KC +0.5 pts
Q4 2:25 Offensive Holding on the Chiefs, 10 yards, wiping out the play +28% DET +2.2 pts
Q4 2:09 False Start on the Chiefs, 5 yards · pre-snap +3% DET +0.2 pts

Lions penalties, every game · Chiefs penalties, every game · All teams, 2023

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 The game turned hereOffensive 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

More from Week 1 2023