Why do some riders gallop stood upright while others crouch down like a jockey?
Standing upright in the saddle while galloping is refered to as “skiiing”. You may see quite a few exercise riders doing that in the US, less so in europe. Sometimes it helps relax a horse more if you stand upright and give the horse its head. Othertimes you stand upright because the horse is a very strong puller and its the only way the rider can persevere for the entire gallop. It is only done at the gallop, when breezing an exercise rider will crouch down like a jockey.