Arena Etiquette goes into play the moment more than one horse and rider are present in an arena. This is a set of written or unwritten rules which are, or at least should be, more common sense than anything. Ride in the same direction. Don't cut someone off. Don't stop abruptly, or back up without looking back first. Slower riders to the inside. The bottom line is safety for both horse and rider. The more horses in an arena, the more important this becomes.
At organized events, be it shows, western gaming, cow sorting, or what have you, there is invariably a "warm up ring". This tends to be a smaller arena, and soon becomes a teeming mass of horseflesh. Invariably, one or two riders enter the fray who are seemingly unaware that they are not alone. They cut in front of others, stop without so much as a "howdy do", and suddenly back their horse without warning. Throw in the newbie rider with no control of a psycho horse they've been "given", shake well, and you can imagine the impending disaster brewing. Oftentimes the ring announcer can be heard bleating something over the PA about safety in the practice arena, but of course, the only folks that hear and heed these announcements are those of us who are already riding safely. Apparently poor riding skills are accompanied by hearing loss.
I make it a point to clear out once the situation begins to approach critical mass, but on at least one occasion, I've made it clear to another that if they cut me off again, things probably won't end well. I have a limited amount of patience, and I'll be darned if I'm going to use it up on people who aren't worthy.
Some horses don't have patience for this either, which presents a whole new set of hazards. During a 4H clinic last year, one of the girls in our club was riding Smokey. Another horse kept riding up on Old Joe and bumping. Now, if Smokey were human, he'd be the guy holding the M1 saying "get off my lawn." He is not particularly fond of other horses, particularly when they are behaving badly. After being bumped twice, he had had his fill.
The third time the offending horse rode up on him, the scene began to unfold as if in slow motion. Subtly, Smokey turned his head to look at Mr. Bumper Car. His pace slowed, his left hip moving ever so slightly to the inside of the arena. Realizing what was about to happen, Mrs. BR began yelling at the girl riding him to watch out, but Paulhamus Arena is rather large, so it's doubtful that she was heard. The distance closed. Smokey cocked his leg, and, at precisely the right moment, kicked out.
Whether he connected or not is up for debate, as the scuffle was over as quickly as it began, with no apparent injury inflicted. However, it could have easily ended in injury to horse or rider, simply because one rider didn't have the good sense to steer her horse clear of the others.
I suspect, that among my readers who ride, I'm preaching to the choir. And of course, oblivious people exist in all facets of life, not just in the warmup arena.