What is "new balls"

Usage examples of "new balls".

That inning he unloosed a few more kinks in his arm and he tried some new balls upon the Bisons.

The smell--crisp, pungent new leather spiced with the acridity of vulcanized rubber seams--brought back memories of the new balls we Fish Hawks were handed on game days at Columbia High as we burst out of the locker room led by Konopski and Basch, the co-captains dazzled by the bright lights and cheers of the packed bandbox gym.