If you've been watching the 2016 U.S. Open, you've probably been thrown off seeing a pair of blue stakes just off No. 9 green at Oakmont Country Club.
No, it's not a hazard, but rather a line of demarcation.
Since the ninth green at Oakmont Country Club doubles as the practice putting green, those blue stakes officially delineate what counts as the practice putting green and what counts as the ninth green. Players who want to practice putting can only practice up to the stakes. However, if a ball from a player on the ninth hole goes beyond the blue stakes into the practice green, they're able to putt the ball on the green where it lies, without penalty.
