When we are covering the base we want to make sure that we stay below the ball. What does that mean to stay below the ball? That means that we start low and stay low on the throw so we can be athletic. If the throw is a good one we want to be flexible and be able to tag quickly. On a bad throw that is going to bounce before it gets to us we want to make sure our glove is below the ball and also on the ground. When the ball bounces we then react to the ball and then either stay down or come up to make the catch.
This video will explain what we mean by staying below the ball on a tag.