If we get all aerodynamic about it, like frisbees and airplanes, baseball movement is subjected to 4 primary forces - thrust, lift, drag, and gravity. With baseballs and frisbess, thrust is provided by the thrower/pitcher. Lift is a function of airflow. With a frisbess, the curved edges provide airspeed increase above the frisbee that causes the lift. Drag comes from below, perpendicular to lift, and is a function of air pressure and, actually, launch angle. Gravity affects the thrown object at 9.8 m/sec^2 with a downward force equal to that constant times the mass of the ball (which is known as the "weight").
The myth of the rising fastball rests on the lift force exceeding the drag force, but this cannot happen due to the weight of the baseball. I wouldn't call that slowing down the descent as much as I would simply being thrown too fast so as to minimize the effects of gravity. Gravitational force does have a time component, like all forces.
The "lack of movement" is about the fact that the launch angle from a pitcher is typically downward, with most release points being higher than the catcher's target. A "rising fastball" is just a fastball thrown at a launch angle with a higher trajectory to above the target. The hitter anticipates the ball being lower than it's actual path, and the 1/2 second doesn't always give the proper time to adjust. The ball isn't rising; it's just following a different path.