Question: After leaving the 7th green, Parrish mistakenly walks to the nearby 18th tee and plays from that tee towards the 8th fairway. He then realizes his mistake. What is the ruling?
Answer: By playing from the 18th tee instead of the 8th tee, Parrish has played from outside the teeing ground of the 8th hole.
In match play, his opponent has the option to let the stroke stand or to require him to cancel the stroke and play from within the proper teeing ground. In this case, as his mistake made the 8th hole longer, his opponent will likely want him to continue to play with that ball!
In stroke play, Parrish incurs two penalty strokes and must then play from the correct tee. If he does not correct the mistake before playing from the 9th tee, he is disqualified. (Rules 11-4 and 11-5)