Many horse trainers won't put two stallions in the same arena because it will usually end up in a fight. My friend, Paul, who is an excellent horse trainer puts two and sometimes three stallions in the same arena. He is very confident in his horsemanship and knows what he is doing. He loves his horses and would never do anything to put them in harms way. You can see him in the background keeping a very close eye on these two horses as they rough it up a bit.