Physioballs, a staple in nearly every training facility, are popular with athletes looking to sculpt six-pack abs, but their benefits go well beyond developing beach muscles.
Their primary advantage is their innate instability. Since they tend to roll during use, they force you to engage stabilizer and core muscles to control your body and prevent the ball from rolling when performing exercises like Push-Ups or Split-Leg Squats. The result is increased strength and balance, which directly translate to on-field skill improvements.
Although physioballs are valuable training tools, they should augment, not replace, a weight lifting program. They will help you develop muscle size, strength and speed, while also increasing balance and stability.
Implement the following exercises in your own program.

Physioball Push-Up

• Assume push-up position with hands on sides of physioball and feet on ground
• Lower with control until chest barely touches ball
• Push up on ball until arms are straight

Sets/Reps: 3×8-10

Physioball Split-Leg Squat

• Assume split-leg stance with top of rear foot on physioball
• Squat until top of front thigh is parallel to floor
• Keep knee behind toes and maintain good posture with shoulder blades squeezed together
• Drive up into start position

Sets/Reps: 3-6×5-8, each leg
 

Physioball Wall Squat

• Place physioball between lower back and wall
• Begin in stance slightly wider than shoulder width
• Lower with control until tops of thighs are parallel to the floor
• Keep knees behind toes
• Drive up into start position

Sets/Reps: 3×10-12
For more inspiration, view additional physioball exercises here.