ok.. i have done it like this.
create an invisible area from the middle to end right or left side, depends on which side you have the ai.
when ball is overlapping the invisible area set enemy "lerp(Enemy.Y, Ball.Y,0.1)"
that will make the enemy follow the ball inside this area. the last bit "0.1" is how fast the enemy will respond on the ball(time), if im correctly.
the only thing i haven't found out yet is how to make the enemy collide with a wall and not go through, because when you lerp an opject then it just ignore everything else.