Are we talking was once a back-up? Cuz there's tons of talented Star QB's that sat initially to learn behind their starter. Marino was initially a back-up. Same with Aaron Rodgers, Tom Brady.
If we're talking journeyman back-up finally gets his shot and shines then Steve Young or Kurt Warner
Could end up being Aaron Rodgers.
Guess it also depends how long they were a backup to rank them in this category/question.
Minimum 2 years...maybe..3..?
One year sitting on the bench shouldn't count right guys?
Rogers sat about 3 years.
Brady sat maybe 1?
Young was a starter in Tampa before going to San Fran and backed up Montana for a few years correct?
Right now I say it's between Young & Rodgers...