Putting The Physics Back Into Football: Short QBs

Almost all of us have heard that scouts and general managers put an emphasis on height when evaluating quarterbacks. However, the question needs to be asked: how fair is the stigma against short quarterbacks? The argument against short quarterbacks has always been, "They can't see over the linemen," but this argument is completely invalid. With the average height of an NFL offensive lineman being 6'5", even the "taller" quarterbacks that are still under the height of 6'5" should be considered too short to play, and being 5'2" is no worse than being 6'4" (the height of Tom Brady). So being that he is not tall enough to see over his linemen, how is Tom Brady still able to play (and win four Super Bowls)?

The same way Russell Wilson has found success in the NFL: throwing through lanes, and anticipating routes. But the fact that taller quarterbacks put up better passing statistics than shorter ones, shows that there may be some merit to the preference for tall quarterbacks. According to ESPN Sport Science, in 2009, quarterbacks 6'4" and over averaged 5% more completed passes and averaged three more touchdown passes than quarterbacks 6'1" and under. But the reason may not be directly linked to their height, but rather the length of their arms; and taller guys tend to have longer arms.

When a quarterback throws a pass, they generate force through their legs and trunk and send it though the lever that is their arm. The arm will then begin to turn inside the shoulder socket at an angular velocity dependent on the amount of force they generated from the rest of their body. The ball's distance from the axis of rotation, which in this case is the shoulder joint, times this angular velocity is what determines the speed of the ball when it is released. This is similar to of a ball at the end of a string, the longer the string, the faster it can be spun.



Here we have two of the exact same quarterback, that generate the same amount of force from the ground and use the exact same throwing mechanics, the only difference being that one is taller and has a longer arm than the other. Since both generate the same amount of force, both will have the exact same angular velocity and therefore, the ball will be released by each quarterback at the same time. However, the arc which represents the ball path, is much longer for the long armed quarterback, and therefore travels a larger distance in the same amount of time, resulting in greater ball speed. 

The length of the quarterbacks arm also aids in releasing the ball higher off the ground which is key to making short and quick passes. 

All quarterbacks have different mechanics and release points. Players like Tom Brady release the ball high away from the top of their heads, while others like Philip Rivers release the ball only a couple inches above their head. This is all fine as long as they're able to throw the ball in a straight line above the heads of the linemen and make those quick bullet passes. However, this is a situation in which shorter quarterbacks may have an issue.



Taller quarterbacks are able to throw the ball in a straight path while shorter ones with a release point below the heads of their linemen have to arc the ball over the heads of their linemen. This becomes a very big issue when it comes to short passes because it limits the amount of speed the quarterback can put on the ball: too much and the pass will go too far. This causes passes to hang in the air longer and may require a quarterback to throw the ball much earlier. This impractical anticipation requirement often results in bad timing which is crucial in the short-intermediate passing game. So the impairment that short quarterbacks have is not about how far their heads are from the ground, but rather how far their hands are. 


This article was written with the help of Dr. Joseph Murphy

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