Newton's 2nd Law
You hit a handball to apply a force to it. That force accelerates it. "Accelerate" doesn't mean "go faster." Forget that oversimplified meaning: this is the elementary physics of the real world, not adolescent fantasy in the hot-rod world.
Acceleration means the rate of change of velocity. It has a magnitude, and it has a direction. Acceleration might be a decrease in speed, if it's direction opposes that of the velocity.
The force and the acceleration are related to each other by only a constant of proportionality. They are in the same direction. If you double one, the other doubles, too. So, if you know the value of one, you can calculate the value of the other. (The constant of proportionality is defined as the mass of the ball.)
F = ma(Yes, there is a hidden complication or two: the force of gravity acts on the ball, too, as does a bit of air friction as the ball moves through the air.)
So, if you aren't sure of, say, the direction of the acceleration, just think about the force you are putting on the ball when you do the accelerating.
A MATTER OF LOOKING
IN THE NEEDED WAYS
BUT UNTIL WE
DEVELOP THE NEEDED
PERCEPTION, WE WILL