From Longman Dictionary of Contemporary Englishthe ball of the foot/handthe ball of the foot/handHBHthe rounded part of the foot at the base of the toes, or the rounded part of the hand at the base of the thumb → ball
Examples from the Corpus
the ball of the foot/hand• The heel of your leading foot should touch the ground, just before the ball of the foot and toes.• However, I would suggest that you subsequently attack employing the ball of the foot rather than the injured instep.• Calluses grow on the ball of the foot and do not have a nucleus.• Raise your back heel and rest your weight on the ball of the foot.• The jumping turning kick: strike with the ball of the foot, keeping the back leg tucked up. 