Drew Brees, 2009: 70.623% (363/514)
Single Season Completion Percentage at 70.8 percent
76.7% held by Colt McCoy of the University of Texas
Tom Brady's worst record as a starting quarterback was in the 2002 season when he led the Patriots to a 9-7 record.
As far as completion percentage goes, for QBs that started at least 8 games in the 2008 season that was Derek Anderson (started 9 games) of the Cleveland Browns who had a 50.2 completion percentage on 142 completions in 283 attempts. The 2008 Browns were the only team in the NFL that season to have a team completion percentage of under 50 percent. Brady Quinn started 3 games and had a 50.6 completion percentage (45 completions in 89 attempts), Ken Dorsey started 3 games and had a 47.3 completion percentage (43 completions in 91 attempts), and Bruce Gradkowski started 1 game and had a 33.3 completion percentage (7 completions in 21 attempts).
Drew Brees broke the completion record and set a record of 72% recently the 2011-2012 season! :) Saints Fan! :D
The most passes completed in a season by an NFL quarterback is 468. The record was set by Drew Brees for the New Orleans Saints in 2011.
Dan Marino holds the record for passing yards in a season with 5084 in 1984.
The NFL record for most rushing yards in a single season by a quarterback is 1,039, set by then Atlanta star Michael Vick during the 2006 season.