Football is the ultimate team sport, and while the quarterback is the most important player, he still has only limited control of what his team does each game.

We wanted a way to isolate a quarterback's value when he threw or ran the ball relative to what the rest of his team did on every other play. The method for this was to collect data on expected points added (EPA) from ESPN Stats & Information research. Every play has an expected point total based on factors such as down, distance to go, field position, home-field advantage and time remaining. The higher the EPA, the more successful that play was at helping the team score the game's next points.

Basically, if a quarterback had a great season despite not getting much help from his running game or defense, then he'll have a much higher EPA relative to his team's EPA, showing his value, and suggesting that he needs more help around him. Even if the quarterback had an average individual season, a terrible team EPA will prove that he's likely far less of the problem than the rest of the team's flaws.

The following is a look at which 10 quarterbacks were the most valuable relative to their team's performance in 2017. Each quarterback's total EPA (on his passes and runs) was compared to the sum of his offense's EPA on plays not involving him (essentially the running game) and EPA from the defense, special teams and penalties. Things like pass blocking and yards after the catch were not accounted for in the QB's EPA total. Only games where that quarterback played were included in the data.

We want to stress that this is not a traditional value analysis such as what one would look at to decide the league MVP (won by Tom Brady last year). In that case, Brady finished first in EPA by a quarterback (120.4), but because the Patriots were so strong in certain areas (rushing, special teams and penalties), the team EPA was 62.8 (ranked sixth). Thus, Brady produced 57.6 more EPA than his team, which ranked 11th in 2017.

Read through our various categories of passers, or skip ahead to the metric of your choice here:

Note: Each quarterback's total EPA and his team's EPA are listed and the rankings are out of 28 quarterbacks/teams because four teams (Packers, Texans, 49ers and Cardinals) did not have a quarterback with at least 10 starts in 2017.

Most valuable

Alex Smith was a top contender for league MVP in the early portion of the 2017 campaign, and had his first 4,000-yard season. AP Photo/Charlie Riedel

QB EPA: plus-103.6 (third)

Team EPA: minus-55.4 (21st)

QB-added value: plus-158.9

When the Chiefs were 5-0 with the No. 1 offense in the league, Smith was arguably the MVP of the league. Had the defense not blown late leads to Oakland and the Jets in games in which Smith was excellent, he might have gotten a stronger push for the award. Despite the offense's brutal November, Smith finished 2017 with the highest passer rating (104.7) in the NFL to go with his first 4,000-yard season. He finished third in QB EPA behind only Brady and Carson Wentz, but is first here mainly because of how far the defense (ranked 25th) fell after losing Eric Berry in Week 1. If the Chiefs continue to play defense like they did last year, then success won't be tied to switching from Smith to Patrick Mahomes. Things have to get better on defense first.