QBR:
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It incorporates all of a quarterback’s contributions to winning, including how he impacts the game on passes, rushes, turnovers, and penalties. Since QBR is built from the play level, it accounts for a team’s level of success or failure on every play to provide the proper context, then allocates credit to the quarterback and his teammate to produce a clearer measure of quarterback efficiency. It was created to be a more meaningful alternative to the passer rating but has been met with criticism among fans and commentators alike.
Raw QBR = g ( AdjustedEPA)
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Action plays
where g() is a function that scales from 0-100, where 50 is average. Total QBR is the raw QBR adjusted for the strength of the opponent.
EPA is calculated based on the down, distance, and the yard line at snap, with each combination having its own point value. The point values are the average net point advantage the team on offense can expect given the particular down, distance, and field position. For example, a 1st and goal chance on the opponent's’ 1 yard line heavily favors the offense, yielding a positive point value. On the other hand, a 3rd and 9 on the team’s own 3 yard line is heavily negative because it drastically favors the opponent.
The value of each play’s outcome is measured by the snap-to-snap change in expected points. This is called Expected Points Added. The Expected Points Added (or lost) in each play are divided among the contributing players on the field based on the role of each player and the type of play. Deeper throws give a higher share of credit to the QB, while screen passes give relatively less credit to the QB and more to the receiver.
Plays that occur in “trash time” are discounted by as much as 30%. Trash time is measured based on the leverage of each play which is primarily a function of score, time, and field position. Important, critical plays that are likely to change the outcome have high leverage, while plays that occur after the game has largely been already decided have low leverage. QBR discounts low leverage plays, but does not boost credit for “clutch” plays.
After each play’s Expected Points Added is adjusted for difficulty, division of credit, and trash time, it is averaged on a per play basis. This average is further adjusted to account for the strength of opponent. Performance against a stronger defense that tends to allow low adjusted EPA per play is adjusted upwards while performance against a weaker defense is adjusted downwards. The degree of adjustment is in direct proportion to the strength of the opponent.
Lastly, the resulting adjusted EPA per play is transformed to a 0 to 100 scale, where 50 is average. The result can be thought of as a percentile. For example, a QBR of 80 means that the QB’s performance is better than 80% of the game performances by QB’s since 2006. A game QBR of 80 would also mean that, given that QB’s performance, his team would be expected to win that game on average 80% of the time.[5]
Rasser rating:
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The calculation of the NFL passer rating is much simpler than the QBR, as it depends only on aggregate statistics rather than an analysis of each play a quarterback is involved in. However, this calculation is based on purely arbitrary coefficients, and is not based on how the game actually operates. Additionally, [u]passer rating double counts completion percentage, favoring quarterbacks who tend to throw screens and other short passes[/u]. Passer rating is calculated using each quarterback's passing attempts, completions, yards, touchdowns and interceptions, and has a maximum value of 158.3 and minimum value of 0. Passer rating ignores large parts of a quarterback’s performance. It ignores sacks, fumbles, designed runs and scrambles, which punishes mobile QB’s. It also does not put plays into its proper context. For example, a 5-yard gain on second-and-5 is very different from a 5-yard gain on third-and-10. Total QBR takes this into account with EPA. Passer rating treats all yards, whether they are air yards or yards after catch, as equally belonging to the QB.
Best,
Laram
