Size - I'm not going to go into much detail here because I feel size can be overrated and there are certainly more important aspects of a quarterback's game. However, most scouts feel the ideal size for a QB is in the 6'2"-6'5" range and 220-230 pounds. By no means, however, would I exclude anyone simply because they do not meet this standard.
Arm Strength - Obviously, having a strong arm is an advantage in the NFL. The thing I look for here is the ability for the quarterback to throw the deep out pattern and get it to the receiver before the cornerback has a chance to break on it. Most QBs can heave the ball downfield plenty far enough to run the offense, but what separates the men from the boys is being able to throw that out pattern like a frozen rope.
Accuracy - Arm strength is great, but if the ball doesn't end up in a spot where the receiver has a legitimate chance of pulling it in, it won't matter how hard or far it's thrown. Watch where the QB puts the ball. Do his receivers constantly have to go down to the ground or leap in the air to pull in his passes? How well does he lead the receivers? Do they catch the ball in stride or do they have to wait for the ball to get to them?
On swing patterns, is the QB throwing the ball over the proper shoulder of the running back or does he have to turn to catch the ball? These are all key indicators of a quarterback's accuracy. I like to grade QBs on their accuracy in the short-to-intermediate range, with a seperate grade for accuracy on the long ball.
Touch - Every team wants a guy with a strong arm, but there are many times during the course of a game when a quarterback has to use finesse over brute strength. When Brett Favre first came into the league, everything he threw looked like it was shot out of a rocket launcher. But he didn't truly become a great quarterback until he learned to drop the ball between defenders.
Defenses often cover receivers with a cornerback and keep a safety deep to give a little help. The quarterback has to have the ability to get the football over the corners head and down into the receiver's hands before the safety has a chance to break on the ball and knock it down or pick it off. If the QB puts too much on the ball, it will not only clear the corner, it will sail right on past the receiver and possibly into the arms of the safety. If the quarterback eases up too much on the pass, it will never get past the cornerback.
Set Up - Set up refers to a quarterback's ability to drop back and get set to throw the ball. Keep an eye on how quickly he is able to drop back into a passing position after the ball is snapped. Watch his footwork. Is it smooth and quick or slow and clumsy? Once he is in a set position watch his feet. Does he stay calm, ready to throw the ball, or are his feet dancing all over the pocket?
Delivery/Release - Once a quarterback drops back and is set in the pocket, keep an eye on how quickly he can get rid of the ball once he spots a receiver. Some guys appear to be able to get rid of the ball with a quick flip of the wrist while others seem to have a long arm motion that takes considerably more time.
Also watch to see if he keeps the ball up in position to be thrown rather than holding it down by his side. The ball should be up near the QB's ear when he is in the set position, not down by his hip. You want to see a good overhand motion, not sidearm, and keep an eye out for any type of hitch or loop in the throwing motion.
Of course, many of the problems with a quarterback's mechanics can be corrected with good coaching, but it can take considerable time to change habits a player has developed throughout his entire playing career.
Running Ability - Having a guy in the pocket who has the ability to run when the play breaks down is a big plus, but in my opinion, is far from the most important aspects of a quarterback's duties. If two guys are equal in all other areas, I would go for the more mobile QB every time, but things like arm strength and accuracy are far more important. A guy with freakish abilities like a Michael Vick might be a possible exception, but for the most part, speed takes a backseat to accuracy and arm strength.
