The first thing to establish is that you have an adequate back up.
You don't want to fire that QB and make a bad situation worse.
The second thing you need to evaluate is if the QB is moving the team or not.
It has nothing to do with statistics. They can look good and complete passes but there is just no fire.
Personality and how they use that personality and how they communicate in the huddle and get these guys motivated has as much to do with playing the QB position at a high level as anthing.
question: When you have a conservative play call because of the QB, such as Maginni with the Browns, does that affect the QBs ability?
When that position (QB) hold you and the rest of the team hostage. You could have everything in place defensively playing very well, the running game going very well and that position just not up to snuff with the rest of the crew. You got to make a change. You gotta find a way.