Yikes!! Definitely a lesson learned the hard way!
I boarded at one place years ago and was there one day where some newbie horse owners had just trailered in their new horse, and were leading it over to turn it out in the new paddock with a few quiet older paddock mates. They waved to me as they passed and asked "Should we take Dobbin in the paddock on the lead first to meet the other horses and to make sure they'll get along?" I'm sure I stammered out something more polite than "Please don't make me watch someone get killed today!" and explained to them why that would basically be the worst idea ever. The horses in the paddock were pretty laid back, and it wasn't very exciting when I turned him out quick for them, but I REALLY didn't want to take the chance of something happening, and then me being the only one there to deal with it and clean up the mess, so I was glad they asked first!!
When I was in college the one instructor drilled into everyone's heads, if a horse panicked or something happened, you get the heck out of the way! You don't rush to untie it, or console it, or unhook it's hoof out of wherever it managed to jam it into, etc. Most of the time the horse, if it could get itself into that position, it could get itself right back out. And the last thing the panicked horse needed was a panicked person rushing in where they're going to get nailed.
And a young teen girl at my barn last summer was outside and witnessed a stallion try to jump the fence over top of an automatic waterer to get to a mare. The stallion got high centered over the fence, and the young girl rushed in, to do what I'm not sure, and she didn't know at the time either. As she ran up, the stallion bit her right in the chest, and threw her out of way. He managed to get himself unstuck and over the fence, and bred the mare he was after. Luckily the girl escaped with only some horrible scrapes and bruising, but no lasting damage. Another lesson learned the hard way.
When stuff goes pear-shaped, JUST GO THE OTHER WAY!! And fast!!