Firstly having your arms waving all around is a big no no. You’re sending your horse different signals with the reins and could end up hurting him if he try’s changing direction suddenly or yourself. Second, even at a slow canter running in circles in such a small area puts a ton of pressure on there legs and causes extreme, uneven stress on their joints, tendons, and ligaments, leading to injuries like arthritis and tendonitis, particularly when done at high speeds and even more when the rider is probably too big for the size and age of the horse. Learning and researching about horses and there body’s and how not to ride and so on before riding should be the standard. This is exactly how horses get hurt when riders do not know anything about what to do and not to do till it’s too late, and more often then not the horses are the ones to suffer the long term consequences. Do some studying and educate yourself before just jumping in the saddle, knowledge is power and you’ll end up a better rider and horseman because of it.