Yes, that IS dangerous...how do they know they aren't going to run a person over, or clothesline a tied horse, who is standing in a position they can't see until they are there?
Tell the arena officials, and they will usually get someone on that sort of stuff...they can lose their insurance over things like that, if someone gets hurt, so they usually don't take it lightly. If they want to run around between classes, they need to do it AWAY from the trailer area.
I remember at one show I was at a couple years ago, some kids went running around like that, and when they went past a trailer with tied horses, one of the tied horses kicked out at one of the kid's horses causing him to spook and buck his own rider off...After getting yelled at by their parents AND the other horse's owner for their stupidity, AND getting embarrassed by falling off, those kids hung out in the waiting pen between classes, rather than running around like idiots...All I can say, is that it's a good thing the girl wasn't actually injured for her actions...I can't stand going to shows and seeing that sort of nonsense, honestly...maybe that's why I don't show as often as I used to, hahaha. However, I DO try to focus on how my own horse and I are doing, and getting my own 'victories' during the course of a long hot crazy day! Lol!
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."