As of right now only one, Tony Romo. Well actually two if you count Matt Moore in Miami, he will probably start a good number of games this coming season. In the 2011 season Tyler Palko started a few games but did not play well at all. Shaun Hill of the Lions was undrafted and he has started some games for in his career and is one of the better backups in the league. Other recent undrafted quarterbacks who started are Jake Delhomme and Jeff Garcia. Max Hall started some games a couple years ago. Chad Hutchinson played for the Cowboys bout 10 years ago replacing Quincy Carter. Then of course Kurt Warner, Warren Moon and Jim Zorn were undrafted. John Kitna was another undrafted guy, but he hasnt been the #1 guy in years.
Starting QBs ... 1 ... Kurt Warner of the St. Louis Rams that won Super Bowl XXXIV.
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Currently no NFL starting quarterbacks are former Green Bay Packers
Houston Texans
based on calculations from the 2008 season, the average number of interceptions thrown by starting NFL quarterbacks is .83.
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New york giants
There are 3 quarterbacks