Problems just don't happen in the first half hour. Ziz was turned out with a mare and a gelding in a new field a few weeks ago, no problems in the first half hour, brought her in the next day and 2 massive bites on her back, treated those, back she went out in the field (horrible mummy) and came in with bites, kicks, scratches and cuts all over her body. Bites and kicks on her near side, kicks over all 4 legs and it looked like she was pushed into something that cut her as her off side was covered in cuts. 2 really nasty cuts including one wound site (heel) which was really badly cut up with 6 cuts over it. She was booted too, with knee and brushing boots and still got 3 nasty kicks to her legs, the boots had been cut (neoprene damaged) too. Another gelding got turned out in this field, which Ziz is no longer in, and his owners went up with lunge whips and schooling whips to make sure he didn't get the same treatment.
I would separate the field or a section of it with electric tape, if you can't do that, I'd put at the least brushing boots on. I used the combined knee and brushing boots, one was actually folded over when I brought her out so I'd use the separate boots if I had to again.