What he's saying is, consider a course that has 18 holes that are all 340-yard par 4s with wide fairways, no bunkers and no water hazards. That's a par 72, but a scratch golfer is not going to shoot a 72. He's going to get a lot of birdies on those short par 4s. So the course rating is going to be a lot lower than 72. I.e., the course rating depends on the difficulty of the course, not the par.
7/9/14 at 7:39pm