It's all about making the correct reads in certain situations based on what the defense gives you. There's a correct receiver to go to, a correct receiver to check down to, a correct play to audible to, a correct side to switch a run to, the correct way to sell the fakes, etc. McNulty has been in this system for years and apparently grades out better than anyone else. This is what Mac wants, a bus driver. He was the backup last year and will probably start this year. All fine & dandy in practice but how will he perform when the intensity is ratcheted up exponentially on gameday? From what I've observed the last few years, he was significantly below average. Granted it was spot duty, but good god he looked awful. It got to the point where Mac wouldn't let him throw a pass.