If I remember correctly, when I got certified as an instructor, we were told that there are three grips we should recommend: Eastern Grip, Western Grip, and Continental Grip. When I played tennis (literally in the last century) I used an extreme western grip to generate topspin. I cannot imagine using a western grip in pickleball, so I put my index finger on the back of the paddle. I think that’s because it’s how I hold a ping pong paddle.
Anyway, “The Pickler” had this to say about the finger on the back of the paddle: You may notice that some pickleball players put a finger or two, or even a thumb, up onto the face of the pickleball paddle. This is common from pickleball players with a table tennis (also sometimes referred to as ping pong) background. Placing a finger, fingers, or thumb on the pickleball paddle face may give you more control of the pickleball paddle. However, the downside is that your fingers and/or thumb are then exposed to being hit by the pickleball, which could result in some mishits (not my spelling) on the pickleball court.
I have yet to hit my finger.
Anyway, I saw this picture of Agassi holding a pickleball paddle.
So, if it’s OK with Agassi, it’s OK with me!