What does Boxing Day have to do with boxing?
any of variously sized large balls used for doing exercises and for physical therapy
The stability ball is also called a balance ball, birth ball, body ball, exercise ball, fitness ball, gym ball, gymnastic ball, physioball, sports ball, Swedish ball, or therapy ball.
any of various large balls used in exercise routines or physical therapy
Exercise balls are also called balance ball, body ball, fitness ball, gym ball, physioball, Pilates ball, sports ball, stability ball, Swedish ball, Swiss ball, therapy ball, or yoga ball.