luckadjusted

Week 18 2023 · January 7, 2024

Rams at 49ers, Week 18 2023: who deserved to win?

The Rams beat the 49ers 21–20, but it was a coin flip: replayed with the way both teams played, the Rams win 6 of 10. Luck ran their way: drops alone were worth 43 points of win probability to the Rams.

Before kickoff the 49ers were 66% favorites. The biggest swing (Q4, 0:55 left): C. Conley dropped a catchable pass, worth 36 points of win probability to the Rams.

Final

Los Angeles Rams 21
San Francisco 49ers 20

January 7, 2024 · Levi's Stadium · Closing line: 49ers −5.5

Luck index +42 Rams lucky · −42 49ers

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. Rams win 6, 49ers win 4.

  1. 1 LA 28 SF 7
  2. 2 LA 24 SF 10
  3. 3 LA 16 SF 6
  4. 4 LA 20 SF 14
  5. 5 LA 24 SF 21
  6. 6 LA 23 SF 21
  7. 7 LA 19 SF 20
  8. 8 LA 24 SF 29
  9. 9 LA 30 SF 40
  10. 10 LA 13 SF 31

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

Rams win 58% of them, 49ers 42%, counting the 4% still level after regulation as half each. The line is what actually happened: Rams by 1.

Show as a table
Final margin in the replaysShare of replays
Rams by 17+12.0%
Rams by 9–1615.0%
Rams by 1–830.6%
Level after regulation3.8%
49ers by 1–820.4%
49ers by 9–1612.3%
49ers by 17+5.9%

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 +15.3 points to the Rams: the final margin was Rams by 1, without the luck 49ers by 14.3. 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.

  • J. Moody, 38 yds missed · 88% expected
  • Extra point missed · 93% expected
  • Extra point missed · 93% expected
Bar: expected chance of a make. Filled dot: made. Open dot: missed or blocked.

Penalties: Rams 2 for 8 yards, 49ers 5 for 78 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 1:53 Offensive Pass Interference on the 49ers (Deebo Samuel), 10 yards, wiping out the play +6% LA +2.2 pts
Q2 7:48 Defensive Holding on the Rams (Quentin Lake), 3 yards +4% SF +1.7 pts
Q2 5:32 Offensive Holding on the 49ers, 10 yards +3% LA +1.6 pts
Q2 1:59 Defensive Offside on the 49ers (Nick Bosa), 5 yards · pre-snap +3% LA +0.5 pts
Q2 0:02 Defensive Offside on the 49ers (Randy Gregory), 5 yards · pre-snap +1% SF +0.1 pts
Q3 6:17 Illegal Shift on the Rams (Ben Skowronek), 5 yards · pre-snap 0% SF +0.5 pts
Q4 7:49 Defensive Pass Interference on the 49ers, 48 yards +14% LA +3.0 pts

Rams penalties, every game · 49ers penalties, every game · All teams, 2023

When it happened

49ers’ chance of winning

As low as 0% and as high as 91%. 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 49ers were ahead in it, below while the Rams were.
#WhenWhat happenedWin probability forNext drive
1 Q1 1:59 The Rams converted 3rd & 53rd & 4th downs · 40% expected +10% LA LA: Touchdown
2 Q2 6:59 The Rams were intercepted on a well-placed throwInterceptions · 0% expected to stay out of the defense's hands +9% SF LA: Punt
3 Q4 7:49 Defensive Pass Interference on the 49ers, 48 yardsJudgment calls +14% LA LA: Touchdown
4 Q4 5:40 The Rams converted 4th & 23rd & 4th downs · 60% expected +12% LA LA: Touchdown
5 Q4 4:56 The Rams’ two-point try was good3rd & 4th downs · 47% expectedR. McCloud dropped a catchable passDrops · 2 drops on 29 catchable balls before this +20% LA LA: Punt
6 Q4 4:41 The 49ers were stopped on 3rd & 103rd & 4th downs · 30% expected +10% LA SF: Punt
7 Q4 0:55 C. Conley dropped a catchable passDrops · 2 drops on 9 catchable balls before this +36% LA SF: Turnover
8 Q4 0:33 The 49ers fumbled and the Rams recoveredFumble bounces · loose balls are close to 50/50 +15% LA –

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.

  • Brock Purdy (SF QB), out, replaced by s.darnold · 8.4 pts
  • Christian McCaffrey (SF RB), out · 0.7 pts
  • Talanoa Hufanga (SF SS), out (IR) · 0.5 pts
  • Tashaun Gipson (SF FS), out · 0.4 pts
  • Ji'Ayir Brown (SF SS), out · 0.4 pts
  • Ambry Thomas (SF CB), out · 0.4 pts
  • Jon Feliciano (SF C), out · 0.3 pts
  • Arik Armstead (SF DT), out · 0.3 pts
  • Matthew Stafford (LA QB), out, replaced by c.wentz · 4.8 pts
  • Cooper Kupp (LA WR), out · 1.3 pts
  • Aaron Donald (LA DT), out · 0.9 pts
  • Tyler Higbee (LA TE), out · 0.7 pts
  • Ernest Jones (LA LB), out · 0.5 pts
  • Kyren Williams (LA RB), out · 0.5 pts
  • Alex Ward (LA LS), 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

Rams 3% · 49ers 97%

Final margin
Rams by 1
Luck in points
15.3 for the Rams
Luck-adjusted margin
49ers by 14.3
Replay with same day's form
Rams 58% · 49ers 42% 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 · Rams · 49ers

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