There are a few things in the world that I don’t really understand. One of them is linesmen who run when a ball is coming in their direction. If a linesmen is watching the action closely and intently enough to be able to make judgements on whether a ball hits the line or is 1 cm in or out, or hits a blocker’s fingernail on the way, logically they should be able to tell with a great degree of accuracy whether that same ball will hit them. That being the case, the most they should ever have to move to avoid a ball would be one single step, perhaps not with the grace or elegance of a bullfighter, but a single step nonetheless. In reality however, many linesmen run like startled rabbits when a ball flies in their direction. That implies that either they aren’t watching closely and intently in the first place, are watching the wrong thing completely or they have incredibly poor vision. None of these answers provides any confidence in said linesman’s ability to make correct calls.
Another reason why officials should have a coach and should practice.