As a child, I thought that fast bowling is just a matter of running as hard as you can and throwing the ball as fast as you can at the batsman. But as I grew up and started playing cricket myself, I realized that the bowlers who followed my above mentioned technique went for plenty of runs and fast bowling involved quite a bit of science in it.
Lets take the example of reverse swing, the art mastered and introduced by Sarfaraz Nawaz in International Cricket. Pakistani bowlers have always been thought of as the best reverse swing bowlers and that seems true when we see Sarfaraz Nawaz, Imran Khan, Waqar Younis, Waseem Akram, Shoaib Akhtar, Abdul Razzaq and Umer Gul, they all in their times have wiped out many teams within just 2-3 overs with their deadly reverse swing bowling and that is one of the reason Pakistan's bowling has always been considered and rated very high in Cricket community.
So how do they do it? How does a 14 year old boy who even never went to school is seen applying the science and reversing the ball in streets of Pakistan?
Well, the science behind reverse swing is rather very simple, it follows two very simple rule of Physics:
1) For any fluid where the speed is high, pressure will be low
2) Fluid flows from high pressure to low pressure
as Air is a fluid, so its the air that does all the science work, lets see how:
The first thing you need to do reverse swing is an old cricket ball having one side completely shiny and other side completely rough. You may have seen international players spitting on the ball and rubbing it as hard as they can with their towel, well yes, they do it for reverse swing.
One side of the ball is shiny and the other side is rough, now at the shiny side the friction will be lower and on the rough side friction will be high. Due to this, the air speed on shiny side will be greater than that on rough side. Following the principle mentioned above, the pressure on shiny side of the ball will be low and pressure on rough side will be high. Following the second principle mentioned above, the ball will move towards shiny side because pressure on rough side was greater than shiny side. That is called "Conventional Swing" because it goes away from a right handed batsman.
Now, the scenario is changed, the shiny side is on the inside and rough side on the outside. Again following the above principles, the air speed on shiny side will be faster than rough side due to which pressure on rough side will be greater than shiny side and following the 2nd principle the ball will move towards the low pressure ie shiny side. It is called "Reverse Swing" because it comes back in to a right handed batsman.
So that is all science behind reverse swing that Aussies and England could not discover for hundreds of years and a Pakistani discovered it and taught to whole world.
Keep in mind that reverse swing is only done on old ball, it can not be done on new ball, the new ball movement is called "Seam Movement" the science behind which I will explain later. Also, to do reverse swing, the bowler needs to bowl the ball at a very high speed to enable air to apply enough force on ball to move it.