'Need not' is probably not the best construction to use in this example. 'Need not' suggests that an action is not required, but is permissible - your sentence therefore sounds like it is not required to throw the ball in golf (but it can be done). However, throwing the ball is against the laws of golf, so perhaps a better sentence would be 'one must not throw the ball in golf' or 'the ball must not be thrown in golf'

Thank you.

'Need not' (no to) normally has the meaning that something in not necessary, but it is allowed. However throwing the ball is against the rules of golf, so a better sentence might be 'one must not throw the ball in golf' or more, naturally, 'throwing the ball is not allowed in golf'

I would remove the word "to" from the sentence. I feel it sounds more natural as "One need not throw the ball in golf."