luckadjusted

Week 13 2020 · December 7, 2020

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

Bills vs 49ers, Week 13 2020: who deserved to win?

The Bills beat the 49ers 34–24, but it was a coin flip: replayed with the way both teams played, the Bills win 5 of 10. Luck ran their way: injuries alone were worth 5.1 points to the Bills.

Before kickoff the 49ers were 54% favorites. The biggest swing (Q2, 8:54 left): Illegal Contact on the 49ers (Richard Sherman), 4 yards, wiping out the play, worth 16 points of win probability to the Bills.

Final

Buffalo Bills 34
San Francisco 49ers 24

December 7, 2020 · State Farm Stadium · Closing line: 49ers −1.5

Luck index +50 Bills lucky · −50 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. Bills win 5, 49ers win 5.

  1. 1 BUF 30 SF 9
  2. 2 BUF 28 SF 14
  3. 3 BUF 26 SF 17
  4. 4 BUF 38 SF 33
  5. 5 BUF 33 SF 31
  6. 6 BUF 24 SF 27
  7. 7 BUF 29 SF 34
  8. 8 BUF 20 SF 30
  9. 9 BUF 10 SF 24
  10. 10 BUF 24 SF 47

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

Bills win 50% of them, 49ers 50%, counting the 6% still level after regulation as half each. The line is what actually happened: Bills by 10.

Show as a table
Final margin in the replaysShare of replays
Bills by 17+10.8%
Bills by 9–1613.9%
Bills by 1–822.7%
Level after regulation5.8%
49ers by 1–821.6%
49ers by 9–1613.8%
49ers by 17+11.5%

Where the luck was

Take the luck out

The final margin was Bills by 10. Remove the luck, one kind at a time, and it becomes Bills by 4.6.

Each row takes one kind of luck out of the margin. Color shows which team it helped. Luck shares are the fitted ones (how much of each component is luck).

The kicks

How likely each kicker was to make that kick (his own record, the distance and the weather), and what happened.

  • T. Bass, 37 yds made · 92% expected
  • R. Gould, 45 yds made · 79% expected
  • T. Bass, 28 yds made · 97% expected
Bar: expected chance of a make. Filled dot: made. Open dot: missed or blocked.

When it happened

49ers’ chance of winning

As low as 0% and as high as 76%. 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 Bills were.
#WhenWhat happenedWin probability forNext drive
1 Q1 9:23 The Bills were stopped on 4th & 13rd & 4th downs · 68% expected +13% SF BUF: Turnover
2 Q1 7:57 Defensive Pass Interference on the Bills, 25 yardsJudgment calls +7% SF SF: Turnover on downs
3 Q1 1:38 The 49ers were stopped on 4th & 13rd & 4th downs · 67% expected +9% BUF SF: Touchdown
4 Q1 1:34 The Bills fumbled and the 49ers recoveredFumble bounces · loose balls are close to 50/50 +7% SF BUF: Touchdown
5 Q2 8:54 Illegal Contact on the 49ers (Richard Sherman), 4 yards, wiping out the playJudgment calls · 7 flags in 1221 snaps before, position avg 1 per 207 +16% BUF BUF: Touchdown
6 Q2 3:16 The Bills converted 4th & 13rd & 4th downs · 68% expected +5% BUF BUF: Touchdown
7 Q4 15:00 The Bills fumbled and recovered it themselvesFumble bounces · loose balls are close to 50/50 +5% BUF BUF: Touchdown
8 Q4 10:44 The Bills converted 4th & 23rd & 4th downs · 62% expected +5% BUF BUF: 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.

  • Jimmy Garoppolo (SF QB), out (IR), replaced by n.mullens · 4.0 pts
  • George Kittle (SF TE), out (IR) · 1.2 pts
  • Emmanuel Moseley (SF CB), out · 0.6 pts
  • Ben Garland (SF OL), out (IR) · 0.4 pts
  • Jaquiski Tartt (SF S), out (IR) · 0.3 pts
  • Jamar Taylor (SF DB), out (IR) · 0.2 pts
  • John Brown (BUF WR), out (IR) · 0.7 pts
  • Cody Ford (BUF T), out (IR) · 0.5 pts
  • Cameron Lewis (BUF DB), out (IR) · 0.3 pts
  • Tyler Kroft (BUF TE), 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

Bills 91% · 49ers 9%

Final margin
Bills by 10
Luck in points
5.4 for the Bills
Luck-adjusted margin
Bills by 4.6
Replay with same day's form
Bills 50% · 49ers 50% 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 (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 13 2020 games · Bills · 49ers

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