Jordan Spieth grip?

[Mike Thomas (sunmart)]

What is he doing?

 

[Lifter]

Interlocking grip results in the left index finger isolated on top of the right hand. With a golf glove, that left index finger really stands out.

I have an interlock and my grip looks like that. So does Ryo Ishikawa's:

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[Lifter]

Spieth's right thumb also extends diagonally over on the other side of the shaft. John Daly does the same thing with his grip:

John Daly - YouTube

I've heard that placing the right thumb diagonally on the shaft rather than vertically helps promote lag.