Commentating on the incident for Fox, former Ryder Cup captain Paul Azinger said: "That's the most out of character I have ever seen Phil".
Mickelson finished the round with an 11-over 81, and 17-over for the tournament.
It was reminiscent of John Daly hitting a moving ball at Pinehurst No. 2 in the 1999 U.S. Open.
Shinnecock Hills has been ripping apart the world's best players all week and it all must have just gotten to Mickelson. "He's putted bad enough that I think he just snapped at how bad his speed was on that putt". That made for a 14, a total of 83 in the first round, and a withdrawal.
"No question it was going to go down into the same spot behind the bunker and I wasn't going to have a shot". On the 18th hole in the second round, Triplett stuck his putter in the ground as a backstop when his ball was headed back down from the hole.
However, by the time he teed it up on the 374-yard par four at four-over for the day, he was 10-over for the tournament, having bogeyed four of the previous five holes. Instead of waiting for the inevitable, Lefty ran over to the ball while it was still moving. and hit it back at the hole.
"I would gladly take the two shots over continuing that display", he said.
"I know it's a two-shot penalty, and at that time I just didn't feel like going back and forth and hitting the same shot over", Mickelson said after his round. "As a result, he incurred a two stroke penalty for a breach of Rule 14-5".
Strangely, the USGA deemed that Mickelson "played" the moving ball, rather than "moving or stopping" it, which could have brought disqualification into play.