N/S calling all smart people

well like they said above you are really dealing with vectors but if you wanted to simplify it and look at it as a triangle then you can. you are thinking that the distance of side C the hypotenuse is longer than the side B that the runner is traveling and it is. However you forgot about the side A of said triangle. The defender has to travel both A and B to get to the same point the runner will be at. There are two ways to get to the top of the triangle so to speak. You can either travel the side C or you can travel A+B. C is always < A+B.

Again it really isn't this simple as you are dealing with triangles that are not always right angles and the players are both moving which is why we mentioned vectors but I thought I would point out your missing piece.