One of the essential principles of an efficient throwing mechanic is to open the elbow straight back after ball separation from the front hand to a position of 90 degrees in the elbow and 90 degrees in the arm pit. An elbow lower than that will have to come “around” the axis of the torso creating an arm mechanic that increases chances of missing targets laterally. Since this mechanic is essential, the key is now to get to that point as quickly as possible, with no wasted motion that adds unneeded time to the delivery. A common mistake is taking the ball down and around, and looping to get ultimately in that same position to bring the ball forward, so it simply makes sense to eliminate all unnecessary motion.
The following video from ESPN’s Year of the Quarterback details the much publicized Tim Tebow delivery and his “new” delivery unveiled at his pro day in 2010. The criticism of Tebow’s delivery is simply one of physics. It takes longer, much longer, to get the ball out when one takes the ball on a full circle before releasing. Additionally, many players who “loop” the ball down and around like this develop a compensation for the added time by trying to shave some time back off the mechanic by either slashing around laterally off the shoulder which decreases lateral accuracy, or creating a short arm and releasing early which greatly reduces power and velocity as well as accuracy. Pro quarterbacks typically have a release time of about .4 seconds. Tebow is consistently .2 seconds later than that. Considering an athlete can go 8-10 yards in one second, that two-tenths of a second has an exponential effect on delivering the football to a target down field in the right place at the right time.