luckadjusted

Week 18 2023 · January 7, 2024

Chiefs at Chargers, Week 18 2023: who deserved to win?

The Chiefs beat the Chargers 13–12, and it was no fluke: replayed with the way both teams actually played, the Chiefs win 9 of 10. The Chargers had the bounces: injuries alone were worth 18 points of win probability to the Chargers.

An off day for the Chargers: their offense played far below its usual level. In a fresh game against the Chiefs they would win 58% of the time; with this day’s form, 12%. The numbers

Before kickoff the Chargers were 60% favorites. The biggest swing (Q1, 5:14 left): Return touchdown by the Chiefs, worth 78 points of win probability to the Chiefs.

Final

Kansas City Chiefs 13
Los Angeles Chargers 12

January 7, 2024 · SoFi Stadium · Closing line: Chargers −3.5

Luck index +12 Chiefs about even · −12 Chargers

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 9, Chargers win 1.

  1. 1 KC 37 LAC 6
  2. 2 KC 30 LAC 7
  3. 3 KC 33 LAC 14
  4. 4 KC 26 LAC 10
  5. 5 KC 26 LAC 13
  6. 6 KC 30 LAC 20
  7. 7 KC 28 LAC 20
  8. 8 KC 25 LAC 20
  9. 9 KC 9 LAC 7
  10. 10 KC 13 LAC 19

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.

An off day for the Chargers

Their offense played far below its usual level. In a fresh game against the Chiefs they would win 58% of the time; with this day’s form, 12%.

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

UnitThis gameUsual levelBetter or worse than usual
Chiefs offenseEPA per play gained −0.11 +0.18 worse by 0.29
Chiefs defenseEPA per play allowed −0.09 +0.04 better by 0.13
Chargers offenseEPA per play gained −0.09 +0.06 worse by 0.15
Chargers defenseEPA per play allowed −0.11 +0.12 better by 0.23

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

Chiefs win 88% of them, Chargers 12%, counting the 1% still level after regulation as half each. The line is what actually happened: Chiefs by 1.

Show as a table
Final margin in the replaysShare of replays
Chiefs by 17+41.5%
Chiefs by 9–1625.6%
Chiefs by 1–820.8%
Level after regulation1.3%
Chargers by 1–87.5%
Chargers by 9–162.4%
Chargers by 17+0.8%

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 +11.8 points to the Chargers: the final margin was Chiefs by 1, without the luck Chiefs by 12.8. 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, 22 yds made · 100% expected
  • C. Dicker, 49 yds made · 79% expected
  • C. Dicker, 40 yds made · 90% expected
  • C. Dicker, 43 yds made · 86% expected
  • C. Dicker, 20 yds made · 100% expected
  • H. Butker, 41 yds made · 89% expected
Bar: expected chance of a make. Filled dot: made. Open dot: missed or blocked.

Penalties: Chiefs 3 for 57 yards, Chargers 1 for 5 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
Q1 9:11 Illegal Shift on the Chargers (Josh Palmer), 5 yards, wiping out the play · pre-snap +6% KC +2.0 pts
Q2 12:52 Offensive Holding on the Chiefs, 10 yards +3% LAC +0.9 pts
Q2 3:40 Defensive Pass Interference on the Chiefs (Jaylen Watson), 33 yards +5% LAC +3.1 pts
Q2 0:52 Defensive Pass Interference on the Chiefs (Joshua Williams), 14 yards +6% LAC +0.9 pts

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

When it happened

Chargers’ chance of winning

As low as 0% and as high as 78%. 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 Chargers were ahead in it, below while the Chiefs were.
#WhenWhat happenedWin probability forNext drive
1 Q1 5:14 The Chargers were stopped on 3rd & 53rd & 4th downs · 31% expectedThe Chargers fumbled and the Chiefs recoveredFumble bounces · loose balls are close to 50/50Return touchdown by the ChiefsSpecial teams +78% KC LAC: Punt
2 Q2 1:36 The Chiefs were stopped on 3rd & 103rd & 4th downs · 28% expectedThe Chiefs were intercepted on a well-placed throwInterceptions · 0% expected to stay out of the defense's hands +13% LAC KC: Punt
3 Q3 6:46 The Chargers converted 3rd & 83rd & 4th downs · 30% expected +16% LAC LAC: Field goal
4 Q3 4:52 The Chargers were stopped on 3rd & 63rd & 4th downs · 35% expected +10% KC LAC: Field goal
5 Q4 13:43 The Chargers were stopped on 3rd & 73rd & 4th downs · 32% expectedA. Erickson dropped a catchable passDrops · 0 drops on 15 catchable balls before this +11% KC LAC: Punt
6 Q4 7:52 The Chargers converted 4th & 63rd & 4th downs · 35% expected +14% LAC LAC: Field goal
7 Q4 3:26 The Chiefs converted 3rd & 73rd & 4th downs · 34% expected +17% KC KC: Field goal
8 Q4 0:19 The Chargers were stopped on 4th & 23rd & 4th downs · 58% expected +18% KC –

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.

  • Justin Herbert (LAC QB), out (IR), replaced by e.stick · 6.2 pts
  • Keenan Allen (LAC WR), out · 1.1 pts
  • Kenneth Murray (LAC LB), out · 0.5 pts
  • Zion Johnson (LAC G), out · 0.5 pts
  • Deane Leonard (LAC CB), out · 0.4 pts
  • Will Clapp (LAC C), out (IR) · 0.3 pts
  • Patrick Mahomes (KC QB), out, replaced by b.gabbert · 9.0 pts
  • Trent McDuffie (KC CB), out · 1.4 pts
  • Donovan Smith (KC T), out · 1.1 pts
  • Travis Kelce (KC TE), out · 1.0 pts
  • L'Jarius Sneed (KC CB), out · 0.7 pts
  • Rashee Rice (KC WR), out · 0.6 pts
  • Michael Danna (KC DE), out · 0.5 pts
  • Nick Bolton (KC LB), out · 0.4 pts
  • Bryan Cook (KC FS), out (IR) · 0.4 pts
  • Isiah Pacheco (KC RB), out · 0.3 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 83% · Chargers 17%

Final margin
Chiefs by 1
Luck in points
11.8 for the Chargers
Luck-adjusted margin
Chiefs by 12.8
Replay with same day's form
Chiefs 88% · Chargers 12% 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 18 2023 games · Chiefs · Chargers

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