Well, some might not consider it abuse but I consider it exceedingly bad traumatic training.
I breed foals, they have very basic training in that they learn how to pick up their feet, lead and respect humans. Other than that they are left to be young horses until they are three.
They come and go to the field loose because it saves me time in haltering them all so basically the only time they have a halter on is when the farrier is here or the vet for inoculations. I can do what I want with them. I have just started three three year old home bred (TB and WBs) I have had no need to use a back strap, they have accepted the tack with no objection. In a week they are lungeing correctly (not in a round pen) they will follow me into the horsebox, I was leading them around large tractors and trailers today because they were removing the muck heap. No bother, no forcing, no worries on their behalf because they trust me.
That poor foal was traumatised and so mentally exhausted it did not have the energy to object to the woman sitting on it.
Maybe not cruelty in many eyes but some of the worse sort of training.