The baseballs kinetic energy changes into friction.
The baseball is rolling which is having kinetic energy.
And as it rolls in the ground covered with thick grass, frictional force treis to act on the baseball. This frictional force tends to stop the ball by applying a force in the opposite direction to the motion of the moving ball. Thus the ball is eventually stopped by the frictional force acting on it when it rolls on the ground.
This is according to the Newtons 1st law of motion which says that force is required to stop or start a motion.
Thus, the baseball's kinetic energy is converted into frictional energy or force.
