Where do you look? Well, who ARE you?

In the video (15 seconds), the defense concentrates on the ball, and loses track of the player they should be defending. This is a mistake that you don't have to make.

On offense, you should be thinking about the ball first and the goal second.

On defense, you should be thinking about marking players first, and the ball second. The ball can't score without an offensive foot behind it, so worry most about marking on defense.

Nice stop by the goalkeeper as her defense does nothing except watch and dance around a little.