Week 1 2021 · September 12, 2021
No FTN charting for this game (drops and interception-worthy throws are not modelled).
49ers at Lions, Week 1 2021: who deserved to win?
The 49ers beat the Lions 41–33, but the replays call it close to a coin flip: with the way both teams played, the 49ers win 6 of 10.
Before kickoff the 49ers were 76% favorites. The biggest swing (Q1, 0:10 left): the Lions converted 4th & 1, worth 9 points of win probability to the Lions.
Final
 San Francisco 49ers | 41 |
|---|---|
 Detroit Lions | 33 |
Replay with same day's form
Luck index +42 49ers lucky · −42 Lions
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. 49ers win 6, Lions win 4.
- 1 SF 51 DET 23
- 2 SF 33 DET 13
- 3 SF 20 DET 6
- 4 SF 33 DET 23
- 5 SF 35 DET 30
- 6 SF 42 DET 40
- 7 SF 31 DET 34
- 8 SF 20 DET 27
- 9 SF 24 DET 37
- 10 SF 16 DET 40
Your call
Did the 49ers earn it, or get lucky?
Three other ways to ask
Each answers a different question, so none of them replaces the replay above.
Before kickoff
The closing betting line, turned into a probability. What everyone knew before the game.
Same teams, fresh 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.
Only coin-flips re-rolled
Every kick, fumble bounce, drop, conversion and judgment call redrawn; everything else fixed. The narrowest view of luck.
How 4,000 replays ended
49ers win 58% of them, Lions 42%, counting the 3% still level after regulation as half each. The line is what actually happened: 49ers by 8.
Show as a table
| Final margin in the replays | Share of replays |
|---|---|
| 49ers by 17+ | 17.1% |
| 49ers by 9–16 | 16.7% |
| 49ers by 1–8 | 22.8% |
| Level after regulation | 2.5% |
| Lions by 1–8 | 19.2% |
| Lions by 9–16 | 12.2% |
| Lions by 17+ | 9.5% |
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.
The kicks
How likely each kicker was to make that kick (his own record, the distance and the weather), and what happened.
- A. Seibert, 51 yds missed · 68% expected
- A. Seibert, 49 yds made · 71% expected
- R. Gould, 40 yds made · 89% expected
- R. Gould, 52 yds missed · 67% expected
- R. Gould, 52 yds made · 66% expected
Penalties: 49ers 7 for 79 yards, Lions 5 for 45 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
| When | Flag | Win probability for |
|---|---|---|
| Q1 4:08 | Roughing the Passer on the 49ers (Arik Armstead), 15 yards | 0% DET +1.0 pts |
| Q2 6:07 | Roughing the Passer on the Lions (Charles Harris), 15 yards | +4% SF +1.6 pts |
| Q2 0:45 | Face Mask on the Lions (Will Harris), 15 yards | +2% SF +1.7 pts |
| Q3 12:09 | Intentional Grounding on the 49ers (Jimmy Garoppolo), 10 yards | 0% DET +0.9 pts |
| Q3 11:16 | Unnecessary Roughness on the 49ers (Jaquiski Tartt), 15 yards | +1% DET +1.3 pts |
| Q3 10:23 | Delay of Game on the Lions, 5 yards · pre-snap | 0% SF +0.3 pts |
| Q4 15:00 | Illegal Touch Pass on the Lions (Quintez Cephus), 0 yards | 0% SF 0.0 pts |
| Q4 8:57 | Offensive Holding on the Lions, 10 yards, wiping out the play | +1% SF +2.4 pts |
| Q4 8:26 | Defensive Offside on the 49ers (Dee Ford), 5 yards, wiping out the play · pre-snap | 0% SF 0.0 pts |
| Q4 4:19 | Defensive Pass Interference on the 49ers (Deommodore Lenoir), 13 yards | 0% DET +1.6 pts |
| Q4 2:00 | Defensive Pass Interference on the 49ers (Dontae Johnson), 16 yards | 0% DET +1.7 pts |
| Q4 1:06 | False Start on the 49ers (George Kittle), 5 yards · pre-snap | 0% DET +0.3 pts |
49ers penalties, every game · Lions penalties, every game · All teams, 2021
When it happened
Lions’ chance of winning
As low as 0% and as high as 65%. Numbers mark the biggest luck moments, listed below.
| # | When | What happened | Win probability for | Next drive |
|---|---|---|---|---|
| 1 | Q1 12:06 | The Lions were stopped on 4th & 23rd & 4th downs · 63% expected | +7% SF | DET: Missed field goal |
| 2 | Q1 12:01 | The 49ers fumbled and the Lions recoveredFumble bounces · loose balls are close to 50/50 | +8% DET | SF: Touchdown |
| 3 | Q1 9:41 | A. Seibert missed a 51-yard field goalKicks · 68% expected for him, 6 of 12 from 45+ before | +5% SF | DET: Touchdown |
| 4 | Q1 2:37 | The Lions converted 3rd & 83rd & 4th downs · 33% expected | +7% DET | DET: Touchdown |
| 5 | Q1 0:54 | The Lions were stopped on 3rd & 23rd & 4th downs · 63% expected | +6% SF | DET: Touchdown |
| 6 | Q1 0:10 | The Lions converted 4th & 13rd & 4th downs · 76% expected | +9% DET | DET: Touchdown |
| 7 | Q2 13:33 | The Lions converted 3rd & 63rd & 4th downs · 31% expected | +7% DET | DET: Touchdown |
| 8 | Q2 1:20 | Return touchdown by the 49ersSpecial teams | +5% SF | SF: Opp touchdown |
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.
- Taylor Decker (DET T), out (IR) · 1.1 pts
- Tyrell Crosby (DET OL), out (IR) · 0.4 pts
- Richie James (SF WR), out (IR) · 0.4 pts
- Tarvarius Moore (SF DB), out (IR) · 0.3 pts
- Javon Kinlaw (SF DT), 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
49ers 95% · Lions 5%
- Final margin
- 49ers by 8
- Luck in points
- 1.6 for the Lions
- Luck-adjusted margin
- 49ers by 9.6
- Replay with same day's form
- 49ers 58% · Lions 42% unchanged: why
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 1 2021 games · 
49ers · 
Lions
More from Week 1 2021
- Cowboys at Buccaneers TB 31–29 · replay 75% for the winner
- Cardinals at Titans ARI 38–13 · replay 76% for the winner
- Jaguars at Texans HOU 37–21 · replay 83% for the winner
- Chargers at Washington LAC 20–16 · replay 89% for the winner
- Vikings at Bengals CIN 27–24 · replay 81% for the winner
- Jets at Panthers CAR 19–14 · replay 94% for the winner
- Eagles at Falcons PHI 32–6 · replay 70% for the winner
- Steelers at Bills PIT 23–16 · replay 59% for the winner
- Seahawks at Colts SEA 28–16 · replay 63% for the winner
- Browns at Chiefs KC 33–29 · replay 71% for the winner
- Broncos at Giants DEN 27–13 · replay 72% for the winner
- Packers vs Saints NO 38–3 · replay 76% for the winner
- Dolphins at Patriots MIA 17–16 · replay 78% for the winner
- Bears at Rams LA 34–14 · replay 89% for the winner
- Ravens at Raiders LV 33–27 · replay 69% for the winner