Join Date: Nov 2011
Location: Central Oregon, USA
I played polo on a college team and it was so relaxed in terms of attire.
For practices we usually wore schooling breeches or just jeans with either tall boots, or paddock boots and half chaps. For matches we wore white jeans with tall boots and knee pads.
Any ole helmet will do starting out. Find one that fits you and is comfortable.
I highly recommend gloves, too.
I will reiterate, polo, especially at the beginning level, is super relaxed. We had many folks join the team who had never ridden before and they got along just fine in jeans, boot and half chaps, a helmet and gloves. Knee pads were usually the first addition to the basic gear!