Interesting that you mention that because I was thinking the Defining moments would be something that would go along with it
Hmm an easy way to let the user know what helps their QB become better in the clutch without too much drivel..
I am honestly thinking it could be incorporated somehow into Defining Moments but I am also thinking about a way for the Game Clock to Illuminate. That way it conveys in a visual manner that your QB is in that frame of time where his play can increase and decrease his clutch rating. Of course this would change as the scores change.
Another issue would be to make sure that each time you gain the lead and lose it that you aren't given the same boosts in clutch as you may be given for that initial lead or the game ending drive for the win.
Though most of the defining moments seem geared more towards the coach and his approval I do imagine you could come up with a similar system for the QB but that would put a lot of emphasis on the Quarterback in a very frontal type of way, kind of detracts from the main part of the game being geared towards coaching alone. I think the clock illuminating or illuminating your teams icon once you have possession would be a good way to indicate when you're in "The Clutch". If you want to get really crazy you could have clutch times/drives factor into Offensive Coordinator attributes/abilities.
The instruction manual could simply show the rating of Clutch.
Clutch: Your Quarterback is given a rating which can be improved or decreased based on his play in the latter parts of every game. A QuarterBack who drives his team down the field with 2 minutes to go in the 4th will gain more increases towards his Clutch rating than he would had he led the team down the field at the beginning of the 4th.
The same could be applied once your QB gathers a clutch rating large enough to matter in clutch situations (Which again would be signified by the clock/possession of the team being illuminated) by default a standard 50 rating on clutch means no change in play. Meaning if you had a guy who managed to consistently throw picks and blow games late he could fall below 50 and thus perform badly in clutch situations, "Choke Artist".
Once the game has went into that area and you're in a clutch mode your QB will have the attributes raised which the clutch rating affects. Accuracy is one attribute I can think of, perhaps an awareness rating increase as well. So your QB has accumulated a 60 in the clutch he'd be awarded one point towards his accuracy and awareness for example.
Of course my idea and system for this may be a little overdone. I think as a basic 4th QT game ending drive it could be a great addition. The precise calculations and ways to improve the clutch rating would be up to you guys to decide for game balance purposes.