A spin bowler is looking to do a couple of things. First the way in which the ball is “flicked” or “twisted” as it comes out of the hand gets it to follow an unpredictable path in the air. It can be spun using the fingers or flicked using the wrist to impart different directions and speeds of spin.
Secondly the ball is usually intentionally bounced off the ground and the imparted spin causes it to “grip” the surface (or skid off it) and change direction somewhat. How much spin, and at what angle to the ball’s path it is applied determines what will happen.
The batsman tries to interpret what they see the ball doing as it flies towards them in order to hit it. The bowler tries to conceal what they do with ball in order to confuse the batsman. Hopefully to the point where the batsman hits the ball in the air to be caught, or misses the ball and gets bowled, mishits the ball off the edge of the bat to be caught behind, or gets hit on the leg padding while standing in front of the stumps where the ball would have gone on to hit them.
The last thing about spin bowling is the pitch surface. The bowler is looking for uneven or broken bits of ground to land the ball in to make its bounce even more unpredictably.
There is a whole lot of language devoted to describing spin bowling. It’s more of an art than a science.
First, as the ball spins, it is dragging air around it, creating high and low pressure zones on either side of the ball. As air moves from the high pressure to low pressure zone, it pushes the ball in that direction. This is called the [Magnus Effect](https://www.youtube.com/watch?v=23f1jvGUWJs)
More importantly, it adds unpredictability to the bounce. As the ball bounces off the clay, the spin it has will help it dig further into the ground and grip more of the particles. Because the clay has particles of different size and shape, you can’t know how it the ball will bounce off those particles. The idea being something like these [reaction balls](https://www.amazon.com/reaction-ball/b?node=5819910011)
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