One of the challenges umpires have is watching runners tag up. They have to watch both the ball being caught and the runner take off at the same time which can be virtually impossible depending on their positioning. To cope with this, umpires are taught, whenever possible, to get both the runner and the outfielder in their field of vision so they can see both actions occurring at the same time. Infielders should do the same thing.
An example is below. A runner is on third and a ball is hit to centerfield. In this case, the third baseman doesn’t have much to do since the first baseman will be the cutoff man. What he can do is move behind third base and get both the runner at third and the center fielder in his field of vision. He then can clearly see if the runner left on time or too early.
On other occasions, the third baseman will be occupied and won’t be able to do this. The picture below is an example. In this diagram, the runner is tagging up at second base and about to go to third. Here, the catcher has the best view of both the runner and the outfield and therefore becomes the player responsible for determining whether the runner left on time or not.
In this next example, it’s the first baseman’s turn since he can see the runner and the left or center fielder at the same time.
This is one of many instances where the players on the field will have a much better view of the game then the coaches in the dugout. Coaches have to teach their players that this only works if every player is taught and knows that they each have a responsibility and a role to play. It’s one of those many little things that separates a great defensive team from just a good one.