Making them stand still on a throw in?

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Partner last night I've never seen before. I thought it might be an interesting night when I saw the Byron collared shirt and long white lanyard. He's been out of officiaiting for awhile and only works as a sub when someone can't show. I noticed that on throw ins when the girls would line up in a straight line formation he made them all get set and told them not to move before he would give the thrower the ball. The coaches looked confused, too, but never asked me about it. Did this used to be a rule in years gone by? I've never seen this before. The game was such a blow out I didn't bother to ask afterwards. I was just ready to call it a night.