Report: Grossman Starting on Sunday

[GTripp0012]

The correlation between QB rating and completion percentage is well documented. The reasoning is that QBs that complete a high percentage of their passes also throw for more yards per attempt, more TDs, and (usually, though not always) fewer INTs. That's why QB rating has managed to hold mainstream for so long: because it doesn't give 100+ ratings to people who sucked. It gave 100+ ratings to guys who have dominated the defense through completions through yards and TDs.

Also, even one INT probably puts the single game QB rating under 90. Interception percentage is the least correlated with completion percentage. Which is probably the one benefit of using QB rating instead of completion percentage: completion percentage probably overrates the guys who often don't read a defense (Favre, Cutler) before going all gunslinger on us.

But completion percentage doesn't overrate those who check down without reading the defense. Those players likely don't throw for yards or points either.

I did a PFR query, and found one season in NFL history where a quarterback performed well below average, for an entire season, but his completion percentage suggested greatness. It was David Carr's one season under Gary Kubiak, in 2006. Carr was released in the offseason, and his 82.1 QB rating wasn't even the best of his career. This may be the only season in NFL history that qualifies a QB who clearly completed too many meaningless passes (Houston finished 24th in passing DVOA that season).

/rant