Some interesting comments.
It is the farmer in me, having spent my first career in farm management, that probably is the reason I tend to take note of the sex of the animals in a field as well as their breed.
Hunters and riding ponies will usually be fillies or geldings, stallions do not seem to be too frequent grazing loose. These are the animals I would be most wary off.
The owners of these would probably have their mares served at stud farms. It is the wild mountain ponies, welsh ponies and welsh cobs, where the mares run with a stallion as a herd. I have seen a stallion deliver a very strong kick to a mare just too keep her in order. If this kick were delivered to a walker it would definitely smash a femur.
The prequel to a horse delivering this sort of kick is fairly obvious, in its body language, but the obvious thing is not to get into range. I think the main danger if close up to large horses, is the risk of been trodden on. Draught horse are very big and heavy, don't go near them when they want to lie down and have a roll
.
Small, children's riding breeds especially Shetlands can be biters. I have learnt this and more from having spent 45 years organizing horse parades at a county show.
But the most telling lesson from those years, vice and bad behaviour is rare in the horse, though I cannot say that for the 2 legged individuals, who all to often sits upon these gentle creatures.