luckadjusted
NFL Week 9 · 2026

Week 2 2021 · September 19, 2021

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

Chiefs at Ravens, Week 2 2021: who deserved to win?

The Ravens beat the Chiefs 36–35, and the replays lean their way: with the same day's form, they win 7 of 10.

An off day for the Chiefs: their defense played far below its usual level. In a fresh game against the Ravens they would win 62% of the time; with this day’s form, 29%. The numbers

Before kickoff the Chiefs were 60% favorites. The game turned on a luck play (Q4, 1:26 left): the Chiefs fumbled and the Ravens recovered, worth 27 points of win probability to the Ravens.

Final

Kansas City Chiefs 35
Baltimore Ravens 36

September 19, 2021 · M&T Bank Stadium · Closing line: Chiefs −3.5

Luck index +29 Ravens lucky · −29 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. Chiefs win 3, Ravens win 7.

  1. 1 KC 36 BAL 17
  2. 2 KC 33 BAL 24
  3. 3 KC 20 BAL 17
  4. 4 KC 28 BAL 31
  5. 5 KC 31 BAL 36
  6. 6 KC 30 BAL 38
  7. 7 KC 31 BAL 43
  8. 8 KC 30 BAL 45
  9. 9 KC 23 BAL 42
  10. 10 KC 14 BAL 42

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 Chiefs

Their defense played far below its usual level. In a fresh game against the Ravens they would win 62% of the time; with this day’s form, 29%.

33 points apart for the Chiefs: 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 +0.46 +0.23 better by 0.23
Chiefs defenseEPA per play allowed +0.34 +0.15 worse by 0.19
Ravens offenseEPA per play gained +0.34 +0.17 better by 0.17
Ravens defenseEPA per play allowed +0.46 +0.09 worse by 0.37

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 29% of them, Ravens 71%, counting the 3% still level after regulation as half each. The line is what actually happened: Ravens by 1.

Show as a table
Final margin in the replaysShare of replays
Chiefs by 17+4.5%
Chiefs by 9–167.9%
Chiefs by 1–814.0%
Level after regulation2.8%
Ravens by 1–823.2%
Ravens by 9–1619.9%
Ravens by 17+27.9%

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 +2.4 points to the Ravens: the final margin was Ravens by 1, without the luck Chiefs by 1.4. Luck shares are the fitted ones (how much of each kind is luck).

Penalties: Chiefs 5 for 46 yards, Ravens 8 for 55 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 half toward luck; pre-snap fouls, which repeat, don’t count. How calls are valued

WhenFlagWin probability for
Q1 10:36 Offensive Holding on the Chiefs, 8 yards +1% BAL +0.7 pts
Q1 0:44 Offensive Pass Interference on the Chiefs (Demarcus Robinson), 10 yards +3% BAL +1.3 pts
Q1 0:18 Intentional Grounding on the Chiefs (Patrick Mahomes), 18 yards +4% BAL +1.6 pts
Q2 5:20 Illegal Formation on the Ravens, 5 yards · pre-snap +2% KC +1.0 pts
Q2 0:47 Offensive Holding on the Ravens, 10 yards +2% KC +0.8 pts
Q2 0:47 False Start on the Ravens (Marquise Brown), 5 yards · pre-snap +3% KC +0.3 pts
Q3 14:55 Defensive Holding on the Ravens (Nnamdi Madubuike), 5 yards 0% KC +0.3 pts
Q3 11:12 Offensive Holding on the Ravens, 10 yards, wiping out the play +4% KC +1.4 pts
Q3 7:37 Defensive Holding on the Ravens (Marlon Humphrey), 5 yards +3% KC +0.8 pts
Q3 6:09 Illegal Contact on the Chiefs (Tyrann Mathieu), 5 yards +3% BAL +0.8 pts
Q3 3:35 Offensive Holding on the Ravens, 10 yards +1% KC +0.6 pts
Q4 14:13 Ineligible Downfield Pass on the Ravens, 5 yards 0% KC 0.0 pts
Q4 8:29 Illegal Contact on the Chiefs (Tyrann Mathieu), 5 yards, wiping out the play +2% BAL +0.6 pts

Chiefs penalties, every game · Ravens penalties, every game · All teams, 2021

When it happened

Ravens’ chance of winning

As low as 8% 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 Ravens were ahead in it, below while the Chiefs were.
#WhenWhat happenedWin probability forNext drive
1 Q1 14:19 Return touchdown by the ChiefsSpecial teams +17% KC KC: Opp touchdown
2 Q1 10:42 The Ravens fumbled and recovered it themselvesFumble bounces · loose balls are close to 50/50 +6% BAL BAL: Touchdown
3 Q1 6:54 The Chiefs converted 3rd & 23rd & 4th downs · 67% expected +6% KC KC: Touchdown
4 Q4 11:28 The Chiefs were stopped on 3rd & 93rd & 4th downs · 35% expected +5% BAL KC: Punt
5 Q4 5:31 The Ravens converted 3rd & 53rd & 4th downs · 47% expected +8% BAL BAL: Touchdown
6 Q4 3:14 The Ravens’ two-point try failed3rd & 4th downs · 47% expected +6% KC BAL: End of game
7 Q4 1:26 The game turned hereThe Chiefs fumbled and the Ravens recoveredFumble bounces · loose balls are close to 50/50 +27% BAL –
8 Q4 1:05 The Ravens converted 4th & 13rd & 4th downs · 79% expected +7% BAL BAL: 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.

  • Marcus Peters (BAL CB), out (IR) · 1.5 pts
  • Derek Wolfe (BAL DE), out · 0.6 pts
  • Miles Boykin (BAL WR), out (IR) · 0.3 pts
  • J.K. Dobbins (BAL RB), out (IR) · 0.1 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 77% · Ravens 23%

Final margin
Ravens by 1
Luck in points
2.4 for the Ravens
Luck-adjusted margin
Chiefs by 1.4
Replay with same day's form
Chiefs 29% · Ravens 71% unchanged: why
How much of each is luck?

0% treats it as skill, 100% as pure luck. The tick is our fit.

What counts

None by default: our tests measured no carryover after a lucky break. Slide it up to count a break for more than its own swing. 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 2 2021 games · Chiefs · Ravens

More from Week 2 2021