Kyle, what is sport if it is not comparing your standard of play to that of another person or other persons. If you are not comparing your play to others, you are not playing sport. Sure, some might consider golf a past-time or recreation, but recreational golf is not real golf, it is a poor facsimile that exists around the fringes of the golfing world. It is to golf what hitting a tennis ball against a wall is to tennis, or hackey sack is to soccer.
I don't care if you are playing in the US Open or a $2 match against a 18 handicapper, unless you are competing against someone you are not participating in the sport of golf.
I agree with David, playing the course is just a fancy way of saying practice.
I have to disagree with Sean & David here to some extent.
Sure, I understand that comparing your performance to others is one element of sport. But, in many of the head-to-head sports, you can actually influence your opponent's performance. Also, golf is different because most other sports have standardized fields of play, so that the emphasis is solely on the performance of the individuals. To say that you are not playing against the course does a disservice to the game.
Put another way, do you really think a long-drive competition (head-to-head) is more about golf than me playing as a single trying to solve the puzzle of the course. Plus, I'm not just competing against the course, I'm competing against my own expectations of my abilities, and striving for that ideal when I can execute a shot as I conceived it.
Put in a philosophical sense, I'm always competing to see how close I can get to the "pure form" of golf on each shot. You may call that "practice," but I think that neglects why the sport of golf is special, since you are the only one that can affect your performance. If we focused solely on the head-to-head elements, we'd move closer to standardized playing fields and I think the essence of the game would be diminished.
Having said all that, I understand that competition against others does add to the game. But, even in those cases, you strive to be the one who comes closest to that ideal most often. Sure, you can occasionally "win" by playing "less worse" than your opponent, but do you feel fufilled? I've been more pleased in matches when I've played really well, but my opponent was just in the zone.
I think the reason for that is that we always are measuring ourselves against the "form" of the game, regardless of what our opponents do. I think the competition against that ideal is what provides the sporting element in golf, which is why a single player can always be engaged in sport.
Trying to tie this into the original post, I suppose some may think of "in regulation" as the ideal, but it really is just a number based off par, which can be arbitrary. One of my local courses has a 465 yard hole, filled with danger throughout (water / trees in drive zone, OB just left of green). It was a par 5 for years, until one year, the scorecard magically changed to a par 4. Hitting a green in regulation changed completely, but how I play the hole should not have changed at all. From an architectural standpoint, I want a course that provides a varying amount of challenges and risk/reward decisions (i.e chances for me to compete against my established ideal). What is "regulation" will vary according to each person's abilities and expectations of their own game.