At a business luncheon up here in Coffs a woman asked him the origin of his nickname. I think she was an AFL noob and her table had pushed her to ask the question judging by their laughter.
John's slightly awkward response was that he was given the nickname because he ate like a horse. I don't think anyone believed that.
I've heard him say it's because he likes carrots.
I've heard others say it's because he was such a prodigious long kick, ie kicking like a horse.
There's only one reason a guy is nicknamed Horse in a sports team.
The eternal connundrum "what happens when an unstoppable force meets an immovable object" was finally solved when David Hasselhoff punched himself in the face.