It was part of the settlement of a lawsuit years ago.

It looks like Phil put one wedge in the bag for a specific circumstance (maybe a spot where he needed to generate extra spin to stop a ball from skidding across the green). I expect he played the other wedges normally. I'd be interested to know how often he actually used the club.

Phil's an interesting guy. Some tournaments, he will put two different drivers in the bag because of one or two shots that set up better with the second driver.

I'm not sure all these tricks amount to much though. The difference between two clubs for those guys is still within the margin of error on each club. In other words, you still have to hit the ball perfectly to make the trick club do better than the regular club.

I fall on the side of if it's legal, let them use it, otherwise it's not really legal. Surely all the other advances in club technology will overcome a square groove from prior to 1990?

The only advantage Phil has with that club is psychological. He's just gotten into the heads of the other guys. That's what Tiger does so well. It looks like Phil is learning the trick.