The Knuckle Ball and Others
Now we're moving into the realms of really thinking outside of the box. If you give this subject a great deal of thought you eventually arrive at Baseball as offering other options and one of the more interesting if you do your research is the Knuckle Ball. Interestingly I've just done a little research today and came across this link - http://i.ehow.com/images/GlobalPhoto/Articles/4665793/curveball-main_Full.jpg
which is an image of a knuckle ball, but if you research wider you'll soon notice that this image rather resembles the Wrist Spinner grip rather than the majority of other representations of the Knuckle Ball. Also associated with this link is the parent link as such here - http://www.ehow.com/how_4826158_throw-knuckle-curve.html and again if you read the description again it virtually describes a Wrist Spinners grip even down to the fact that you flick the wrist! So as you can see there's a degree of interesting cross-over going on and it's something I feel that can add to your potential as a Wrist Spinner.
My own variation which is very much developmental is based on the images found here at wikipedia http://en.wikipedia.org/wiki/Knuckleball the tips of my fingers are bent very much inwards with the ball secured resting on the actual knuckles in the side shot here. When I get a chance I'll shoot some images of my knuckle ball and upload them. But with regards a description of my version the main thing I find is that it's a faster ball with a flatter trajectory. The interesting aspect for me is the claim that when bowled with the smooth side of the ball facing the bat and the seam at the edges there's the potential for the ball to drift - but not in one single direction but in two directions so that the ball across 22 yards may wobble significantly from one side to the other. This is so extreme in baseball that the Knuckle Ball poses difficulties for the catcher who wears those enormous big catching mits!
I'm probably going to include some of the Finger Spin techniques in this section including the Iverson Gleeson technique which has found popularity recently via Sri Lanka's Ajantha Mendis who seems to have renamed it the Carrom Ball.