<P> 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 . </P> <P> 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 . </P> <P> 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 . </P> <P> 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 . </P>

Who has the highest qbr rating in the nfl