Here is Yasir Shah, tucking his thumb inside. 
http://www.espncricinfo.com/pakistan/content/story/970079.html
I cannot get my index and middle finger the slide across the ball like that and fully engage the ring finger.
Is it to do with wrist position?.
				
			http://www.espncricinfo.com/pakistan/content/story/970079.html
I cannot get my index and middle finger the slide across the ball like that and fully engage the ring finger.
Is it to do with wrist position?.
 ) struggling with. I just want to add that try to keep front hand straight and take that till thighs and this will add to overall progress.