In simple terms the ball will only change its flight path to the batsman when the air around the surface of the ball travels at different speeds.
Remember the ball is pushing air to the side as it travels forward. Why? Because the air must go somewhere.
Check out why aeroplanes take off or why yachts go forward into the wind! Or let a piece of paper drop from your fingers and then blow over the bend of the paper.
See the paper come up? This is because you have fast air on one side and slow air on the bottom side and the paper is "sucked" into the faster air current or flow.HOPE IT HELP PLZ MARK AS BRAINLIEST