Here's my attempt at a simple explanation:

Most of the time, Justin wouldn't brag about breaking 100 because that's not a good score.

The average golf course is usually around a par 72 which means if you shoot 72 you broke even. Professional golfers shoot under par which explains why their best scores are negative numbers such as -6. Since Justin has a 6 handicap, that means if he's playing with someone whose better than him such as Tony Romo, he gets to subtract 6 shots off his score while Tony would only subtract 3 with his handicap. It's to make the game more competitive.

Justin usually shoots in the high 70's, low 80's on a regular golf course. The US Open course is obviously much harder so in this case, he's probably happy with his 98.

I hope that helps a little. image