In my opinion, throwing the ball is an important football skill for quarterbacks to have when trying to get the ball to their wide receivers. By throwing the ball through the air, the ball travels more quickly than if you ran over and gave them the ball. Therefore, it is an important thing for quarterbacks to be good at.
Mike Glennon had some issues trying to throw the ball.
(Danke schoen to Buzzfeed Sports)
The problem here is that he was unable to throw the ball. It is supposed to come out of your hand and go forwards, instead it goes in no direction whatsoever. If I were Mike Glennon's coach, I would make him practice throwing the ball.
Of course, since the ball came out of his hand before it went forward, this is a fumble, recovered by the Panthers.