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In the following video clip, this will demonstrate why we must have ball status at all times when working a softball game, regardless of the level of play. This video appears to be a recreational level game of 10u-12u. There are runners on 2B and 3B with the umpire positioned behind the shortstop as expected.
The pitcher delivers the pitch and the catcher after receiving the pitch makes an attempt to throw out the runner at 3B. The ball is not caught and goes into LF where the fielder retrieves the ball. As this is happening, the BU begins to walk forward toward home-plate as the runner at 3B is now heading home.
The BU takes a few steps and gets into a 'set' position, all without knowing where the ball is. The fielder attempts to make a throw to home, but the ball is offline on the throw and strikes the umpire in the back of the head causing him to fall to the ground.
This is a simple case of not being aware of the surroundings and taking for granted that the play will happen as you expect it.