The correct relationship is: As the ball’s potential energy decreases, its kinetic energy increases.
When a baseball is at rest, it may have some potential energy due to its height above the ground. When it is thrown, its height may decrease (if we assume it’s being thrown towards the ground), which causes its potential energy to decrease. At the same time, the energy put into throwing the ball converts to kinetic energy, causing the ball to move faster, thereby increasing its kinetic energy.