When people talk of visual requirements, they usually refer to the visual requirements of the player - things like having good visual acuity and peripheral vision. I tend to approach it another way, by looking at the visual requirements of the sport itself.
For a hooker, one of the main requirements is to be able to throw a ball into a lineout in such a way that it can be caught by the intended player on your side, and not intercepted by the opponents. Of course, it’s not always the hooker’s fault when this doesn’t happen, as it’s very much a team effort between thrower, lifters and catcher, and also depends on the ability of the opposition to defend.
One of the main difficulties for hookers is that they don’t actually have a target to aim for. They’re aiming for a space above the catchers head. But if it’s a throw towards the back of the line out, they often have to throw the ball in a parabola to evade the opposition’s catcher in the middle. If that’s someone like Devin Toner, who’s nearly seven feet tall before he’s lifted, that’s not an easy task.
You can get hookers to practise their throwing by aiming at a mark on a post, and that would certainly be better than nothing. But the best way to practise getting the correct trajectory for deeper throws would be to throw the ball through a hoop. The hoop would be set at the height of the opposition’s front jumpers.
I’ve seen this done with a tyre suspended from the cross bar. But ideally you’d want this to be hoop on an adjustable stand, and you’d want a second one set for the height of your tail catcher. The hooker then practises getting the ball through both hoops. This can be done as an individual practice, just with one set of forwards, and as fully contested lineouts.
The hooker should also spend some time throwing whilst blindfolded, giving the brain a chance to concentrate on the kinaesthetic (muscle) feedback with each throw. The position of the hands holding the ball, especially the little finger, must be identical each time (see earlier blogs).
The visual requirements of hooking the ball are minimal, certainly at elite level, because there’s hardly any hooking these days. Put-ins are still as straight as a dog’s hind leg, so it’s more important to push than to hook the ball. I read that Sean Fitzpatrick used to practice with his eyes closed, so he could still hook the ball even if he couldn’t see it because he was pushed out of position by the opposition scrum. Unless or until referees insist on the put-in being straight, I can’t see many people practising that today.