Phil Mickelson was able to completely change the model of his Callaway golf ball during his opening round at the US PGA Championship because the PGA of America does not run with the 'One-Ball Rule' like they do on the PGA Tour.
This was pointed out by the Phil Mickelson Tracker account during the first round at Oak Hill.
On the PGA Tour, this would have broken the rules. But the PGA of America is not playing by such rules.
There is no one ball rule at the PGA— Phil Mickelson (@PhilMickelson) May 19, 2023
"Noticed Phil has changed balls mid round," tweeted the Mickelson fan acount.
"Was using a Callaway that he lined himself with sharpie, now using the official triple track ball."
After the round, Mickelson personally responded to clarifiy the rule via his own official Twitter account.
Mickelson, a two-time US PGA champion, said: "There is no one ball rule at the PGA."
The 'One-Ball Rule' not only comes into play on the PGA Tour but also a number of other competitions.
It falls under Model Local Rule G-4.
The PGA of America have just decided not to play by those rules at the US PGA.
Should Model Local Rule G-4 ever be called into play by your tournament committee, then it will mean you can only play with the exact same brand, make and model of golf ball all the way through the round.
It can be a different number, though.
If you switch to play a different golf ball during the round then you will receive a two-stroke penalty for every stroke made with that golf ball.
We recently spoke at large about the 'One-Ball Rule' in a rules article, which you can read below.
Mickelson ended up shooting an opening round of 73 and he added a 72 on Friday to fall back to 5-over par.
That will just sneak into the weekend.
Since moving to LIV Golf, Mickelson's long-time sponsor Callaway decided to pause their relationship with him.
Mickelson still plays with a majority of Callaway clubs and obviously still uses their golf ball, but he has recently switched into the TaylorMade BRNR Mini Driver, which we recently tested out.
You can watch our review here: