Potential energy is stored energy that has the potential to transfer into kinetic energy.  When the ball is hit into the air, it gains potential energy until it begins to fall.  

The equation for potential energy is:

Potential Energy = Mass x Freefall acceleration x height

PE= m x g x h

Example Problem:  If the ball has a mass of 10 grams, and a freefall acceleration of 9.8 and it is 10 feet in the air, what is it's potential energy.

PE= m x g x h

PE= 10g x 9.8 x 10

Answer: PE= 980