There’s abuse in every riding discipline and is something equestrians have been working to limit for a while. While I don’t see polo itself as being abusive or cruel to horses, it is a lot more intensive then other sports and thus some horses may not find it as enjoyable.

What you experienced was a very loyal and well trained horse. Polo ponies are known for this. Having met people who’ve worked with them, they have pretty intense training schedules and require a pretty specific skill set. In a higher level game, the horses tend to be swapped out very regularly so that they aren’t overworked and thus each rider has an insane number of mounts with them for each match (I think it’s something like 4 to 7, but not sure). Compared to other disciplines, these horses get up close and personal with each other and as such are well socialized. However, it can still be stressful for a horse to get right up next to an unfamiliar horse. They are incredible horses with incredible training in a very interesting sport.

It’s a very different sport. What you saw were these differences in action. Doesn’t make it abusive. Because a mane is shaved and a tail is braided doesn’t mean a horse is unable to express their discomfort. I see show jumping and polo on the same level of ‘cruelty’ (if we’re going to use that word) since both require the horse to go full stop and have a higher chance of injury compared to something like english pleasure or trail riding.