Stephen A. Smith explains why Aaron Rodgers should still be considered one of the best quarterbacks of all time despite the Packers' struggles this season. (0:55)

Any given Sunday ... every quarterback has a shot to sit atop the Total QBR leaderboard. While QBs are most often judged by wins and losses or touchdowns and interceptions, we like to rank them every week by the stat that measures their per-play contribution to their team's cause.

An explainer of QBR can be found here, but the main idea is to capture more elements of a quarterback's play than traditional methods consider. QBR includes the value (or lack thereof) of quarterback rushing, sacks, fumbles, relevant penalties and -- crucially -- the down and distance of every play. QBR works on a zero-to-100 scale, with 50 being roughly average and 75 about Pro Bowl-caliber.

Each Tuesday in this space, we'll highlight the best and worst QBR performances from the NFL weekend and break down what made each quarterback perform at either extreme.

Which quarterbacks were the best and worst in Week 15?

Top three

Total QBR: 87.0

Though Darnold has struggled from a production standpoint this season, smart analysts have pointed out signs of greatness from the young quarterback throughout the season.

On Saturday against the Texans, it came together, even in a losing effort. Darnold's success on third down (97.4 QBR in those situations) fueled him to his second-best QBR game of the season, just narrowly falling short of his Week 6 performance against the Colts.

Darnold and Giants running back Saquon Barkley will forever be linked given their teams' proximity and the way they were drafted, but on this weekend, the Jets got the better end of the deal. -- Walder

Sam Darnold Week 15 Pass Plot Completions Attempts Yards TD INT 24 38 253 2 0

Total QBR: 81.5

Stafford did most of his damage on the Lions' two scoring drives in the second quarter, largely using big plays to Kenny Golladay.

The duo hooked up seven times on eight attempts for 146 yards and five first downs overall. Five of Stafford's largest six plays in terms of expected points added came when Golladay was the target. Three of those completions came in that two-drive span totaling 95 yards.

Their biggest connections came while trailing 7-6. Stafford hit Golladay for a 24-yard pass on a third-and-10 and then found him for a 40-yard gain on a third-and-7 later in the drive. Those hookups helped set up a go-ahead touchdown that ultimately proved to be the Lions' final points of the game. -- Gargiulo

Matthew Stafford Week 15 Pass Plot Completions Attempts Yards TD INT 22 29 208 1 0

Total QBR: 79.9

The comeback charge led by Rivers to beat the Chiefs on Thursday night catapulted the veteran QB into the MVP debate. The game also was a testament to QBR's value, which recognized Rivers' strong performance despite the fact that he threw two interceptions.

Though QBR awards no extra credit for high-leverage situations, it does keep the clock in mind in determining the expected points added of a given play. With the game winding to a close, Rivers and the Chargers faced first-and-goal from the 1-yard line. But because there were only eight seconds remaining, QBR is aware that they did not truly have four end zone shots at their disposal. When Rivers connected with Mike Williams for the touchdown, it launched his raw QBR from 53.6 to 73.0. A few seconds later, the two-point conversion brought the number to 75.7, which was then adjusted up a few points on account of opponent and game location.

Rivers now trails only Drew Brees and Patrick Mahomes in Total QBR this season. -- Walder

Philip Rivers Week 15 Pass Plot Completions Attempts Yards TD INT 26 38 313 2 2

Just missed: Deshaun Watson, Houston Texans (78.3); Matt Ryan, Atlanta Falcons (73.4)

Bottom three

Total QBR: 3.1

Rosen now owns three of the five worst single-game Total QBRs of the season after finishing Sunday with a 3.1. He ran the gamut of bad plays that led to his single-digit QBR against the Falcons, from interceptions (two) to taking sacks (six) and fumbling (only one of those).

His most damaging play, in terms of expected points added, was his first-quarter interception. Leading 7-0 and approaching midfield, Rosen attempted a pass to the flat that was first tipped by a defender before being picked off and returned for a touchdown. That turned what was a promising start into a hole that he was unable to dig out of, never having his raw QBR reach 20 for the remainder of the game. -- Gargiulo

Josh Rosen Week 15 Pass Plot Completions Attempts Yards TD INT 13 22 132 0 2

Total QBR: 6.5

After back-to-back weeks with a Total QBR in the 70s and three straight overall above 50, Tannehill regressed to his pre-injury self, finishing with a 6.5 against Minnesota. It was his second-worst Total QBR of the season (4.2 against New England in Week 4) and third worst of his career.

It is easy to see by looking at the box score why Tannehill was in single digits, as he was sacked a staggering nine times, four of which came on third or fourth downs. Even if we discard his nine sacks, Tannehill wasn't very efficient. He had a raw QBR of just 21.2 on his non-sack pass attempts and rushing plays. -- Gargiulo

Ryan Tannehill Week 15 Pass Plot Completions Attempts Yards TD INT 11 24 108 0 0

Total QBR: 14.2

Unfortunately for Newton, there is no injury adjustment in QBR. An injured shoulder hindered Newton, and it showed. It showed watching the game; by the end he could barely fire a fluttering pass to his receivers. And it showed in the pass chart below.

Newton was just 1-of-6 on passes 10 or more yards downfield on Monday night, including one crucial interception thrown to Eli Apple in the end zone. While there are passers who thrive on quick, short throws in the NFL, it's hard to have success without doing a little better than that on at least medium-distance targets. -- Walder

Cam Newton Week 15 Pass Plot Completions Attempts Yards TD INT 16 29 131 0 1

Just missed: Eli Manning, New York Giants (19.3); Josh Allen, Buffalo Bills (19.6)