Since this team has a great history of QB busts this should be something we can define easily. But it really isn't.
To me, it is if the QB fails to achieve a level of success equal to the position he was drafted. This is a definition of a bust at any position but the QB is more visible so when he fails it is much more noticeable. So while a defensive lineman or a wide receiver may be a bust it rarely effects a team like having a bust at the QB position. A QB may perform ok but not up to expectations. Someone like Alex Smith in San Francisco or Sam Bradford in St. Louis could easily be called busts but they are still playing, at times well, with other teams. So in the true sense they weren't total busts but they certainly didn't live up to their top of the draft billing when picked. Grossman was a bust being a first round pick that never panned out. Hell, we could call Jim McMahon something of a bust as well. Yes he led us to the Superbowl but he never did play well after that. Lets remember he was the number 5 overall pick in 1982. He certainly doesn't have the body of work to support his adoration here but for a championship starved city he became a demi-god. But he never lived up to his potential.
As for Trubisky, we will won't really know if he is a bust for us until probably midpoint next year. Nagy's system is very complex and even an experienced QB like Alex Smith had to learn to implement it. If you look at his early numbers in 2016 they weren't that much different from Trubisky's right now. They were better than Trubisky's but Alex Smith in his first four games with Nagy as OC averaged around 240 yards per game with 5TDs and two INTS. His first two games had him with one big game and one less decent. So my jury is still out on an inexperienced QB with a lot of the strengths of an Alex Smith and maybe some of his weaknesses. It is honestly hard to tell at this point.
