Well it looks like he is leaning a little into the barrel. that's a nono becase it can case a horse's legs to slip out from underneath him.
He looks like he's trying to get his legs down but he just can't with the ground.
I also don't like how he is gaping his mouth, because it means he is avoiding the bit. Which may mean a few things like you are putting too much pressure on his mouth, he dislikes the bit, or he has teeth issues. Or it could be a different issue.
I would probaby do better if there were side shots from a different point.