Speedy, you're a better rider than about 99% of the planet if you can sit a fallen, sliding horse. I don't see where he's a 'pathetic' rider at all.
These are snapshots in time. I'd like to see the whole match, in order to decide whether or not he deserves the 'abusive' title they're throwing at him.
Don't the riders have a string of 7 or 9 horses for each match? I'm not sure of the exact number, but I know they don't ride just one horse for the whole game.
Polo's a rough sport, and horses and riders collide and jostle each other. There's no telling, unless you were there, how that horse got its injury.