28 kinds of ball games, including handball, basketball, football, volleyball, badminton, tennis, golf, ice hockey, beach volleyball, baseball, softball, rattan ball, shuttlecock, table tennis, billiards, cuju, cricket, squash, casserole, curling, gateball, rugby, hockey, water polo and polo. Sphere set definition: 1. The set of points whose distance to a fixed point in space is equal to or less than a fixed length is called a ball. 2. With the straight line with the diameter of the semicircle as the rotation axis, the rotating body formed by one rotation of the semicircle surface is called a sphere, which is called a ball for short. 3. A point set whose distance from a fixed point in space is equal to a fixed length is called a sphere. 4. Weigh the center of the ball at a fixed point and the radius of the ball at a fixed length. /iknow-pic . cdn . BCE Bos . com/2934349 b 033 b 5b b5 bb 5c 3 c 5 1f 038d 3d 539 b 700 BCD 0 " target = " _ blank " title = " " class = " ikqb _ img _ alink " & gt； /iknow-pic . cdn . BCE Bos . com/2934349 b 033 b 5b b5 bb 5c 3 c 5 1f 038d 3d 539 b 700 BCD 0？ x-BCE-process = image % 2f resize % 2Cm _ lfit % 2Cw _ 600% 2Ch _ 800% 2c limit _ 1% 2f quality % 2Cq _ 85% 2f format % 2Cf _ auto " esrc = "/ N2/20 17/ 1009/c 172848-30808608 . html " target = " _ blank " title = " People