I actually think that goal kicking is the one part of rugby league that is the most affected by nerves, because the player has a lot of time to think about it. You need to learn to kick the ball rather than the goal, and close out of your mind what is riding on it. Having all that time to take a shot can make your mind cluttered, doubt can creep in, you can start thinking about the result of the kick, rather than the process. I can't be sure that's what happened with Croker, but I'd think so. He would normally eat those for breakfast, from what I've seen.