Playing quarterback at the NFL level is akin to trying to compute some pretty complex problems while being chased by a gang of thugs looking to beat your brains in.
There is a reason it is called the toughest position to play in sports, as well as a reason that there are far fewer than 32 guys in the country that teams are happy to turn over the keys to the franchise every week.
Mike Mayock, who does some Minnesota Vikings preseason games, remarked a couple of seasons back that he thought he was pretty up to speed with what quarterbacks were expected to do at the NFL level until he sat in on a Vikings QB meeting before the game. He said he was astonished at the sheer volume of information they were expected to be able to process in split seconds before and after the snap, and this was the offense of Brad Childress and Darrell Bevell.
The bottom line is that no matter how hard you think being a QB at the NFL level is, it's harder!
Given that there is so much these guys have to be able to do, the most important of which is avoiding negative plays, it's no surprise that you can pinpoint several recurring mistakes that are made, especially by young players. The more experienced the players get, the more likely any mistakes that they make are less to do with any inherent flaw in their play and more to do with being outfoxed on individual plays.
The Speed of the Game
This is a term that is thrown around a lot when people talk about young quarterbacks making the leap from college to the NFL. Some guys like Cam Newton have the kind of size and speed that transcends that gap, but for most ordinary people there is a serious jump in speed that can mess with quarterbacks in a few different ways.
The first and most obvious way is what I call Christian Ponder Syndrome after his rookie year—where a quarterback hasn't yet learned that at this level he is no longer a faster and better athlete than most of the people chasing him.
Guys like Christian Ponder may be comparatively impressive athletes and be able to beat most guys in college, but in the NFL they slip way down the totem pole. At this level they might be better termed mobile, but they're no longer better athletes than some of the super athletes manning the defensive line and chasing them around the backfield.
The number of sacks and hits that Ponder took as a rookie because he took off and just wasn't used to being chased down from behind was ridiculous.
The last thing any NFL team wants is its quarterback being exposed to unnecessary hits, so getting them used to the difference in speed and athleticism of defenders, especially if it now means they can't just take off and be safe, is a big deal.
The next place where the speed of NFL defenders raises problems is in the actual passing game. With zone coverage plentiful at this level, quarterbacks have to see holes before they open and get the ball to the receiver in those holes before they close again.
You ever see those elaborate reaction-testing rigs where a person stands in front of a wall with lights flashing at random that they need to hit before they stop flashing? That's kind of like what a quarterback is doing back in the pocket. He needs to be able to see the hole and deliver the ball before that window closes.
At the NFL level those windows are not open for long, and players in coverage have a much greater ability to read and react, covering serious distance while the throw is in the air. So many of those ugly throws you see from young quarterbacks are against zone coverage where they have just missed their window—thrown late or having never seen a guy in coverage to one side of where they are looking to throw the ball, so intent were they on hitting their guy.
Staring Down a Target
That brings us to our next most common issue for quarterbacks, and though this is most common with young guys, it is by no means limited to them, and at times all quarterbacks are guilty of this one—staring down their target.
As a defender in zone coverage, nothing gives you the ability to set off to the right spot on the field faster than the quarterback telegraphing the throw he wants to make by staring down his target. If his eyes never move from the guy he wants to hit, you can set off as early as you like to get between him and his receiver to intercept the pass and take it in the other direction.
Most of the really ugly interceptions you see in the NFL come because the quarterback's eyes never left his intended receiver, and a player that should have had nothing to do with the pass on paper was able to read it and cover ground to get in the way.
At this level you need to be able to use your eyes to freeze players in coverage to ensure that they can't react to where you're looking and have to maintain their assigned zone in coverage rather than gambling and taking off towards one particular receiver.
Even cornerbacks can be tipped off by what's coming if they aren't forced by the quarterback to respect the fakes or subtle moves the receiver is throwing at them. A corner backpedaling in zone coverage can allow his receiver to get behind him—a cardinal sin otherwise—if he can tell from the quarterback that the receiver isn't going deep, but rather is pretending he is before he breaks back towards the sideline or the pass inside.
Asante Samuel has perfected this art of breaking on out patterns and cutting underneath receivers because he was able to read the quarterback and take off before he should have been able to.
Staring down targets is an invitation to defenders to get involved in the party in a way the offense doesn't want.
Simply Misdiagnosing the Coverage
At this stage, NFL offenses have a lot of advantages inherently in the rules with the amount of contact permitted and what they can take advantage of to make plays. NFL defenses can't attack back the way they used to be able to, so they're left with more subtle ways of combating modern offenses.
Instead of getting physical and trying to beat them up, they're moving to deception and trickery. You don't need to bully a receiver out of his route and timing if you can bait the quarterback into thinking a guy will be open and then shut it down when he's committed to throwing the ball that way.
There are only so many coverages that can be run, and NFL QBs know them all intimately, so the modern passing game has become a complex chess game of moving pieces immediately before and after the snap where defenses try to convince the offense that they are running one coverage but actually run something completely different.
This is why you will see safeties moving around before scurrying back into a zone immediately after the snap, or players rolling away from where they lined up into a different zone. The aim of the game for the defense is to fool the quarterback, and his job is to try to see through the deception to what the actual play call is.
Perhaps more picks come from simply misdiagnosing the coverage than any other mistake at this level, and the best quarterbacks are the ones that can read things without thinking and get it right every time. It is very difficult to fool Tom Brady or Peyton Manning with any kind of pre- and post-snap movement, but it won't stop teams from trying.