A ball game-related training system comprising: a play field defined by a half line, both opposing end lines, and both opposing side lines, wherein the play field has a net extending along the half line; a vertical column structure adjacent to at least one of the end and side lines; and a ball supply apparatus coupled to the column structure at an upper portion thereof, wherein the ball supply apparatus includes: a housing coupled to the upper portion of the column structure, wherein a top portion of housing is partially open, wherein the housing is divided by a partition into a ball storage portion and a ball discharge portion, wherein a bottom face of the ball storage portion is inclined downward toward the ball discharge portion, wherein a first opening is formed in a bottom of the ball discharge portion, and a second opening is formed in the partition at a lower portion thereof; a rotatable opening/closing plate rotatably coupled to the partition, wherein the rotatable opening/closing plate is configured to rotate to open/close the second opening; and a ball discharge tube rotatably coupled to the ball discharge portion at the first opening, wherein the ball discharge tube ball-communicates with the ball discharge portion via the first opening, characterized in that the upper end of the discharge tube is inserted into the ball discharge portion through the first opening, wherein a straight bevel gear system is disposed in the housing, wherein a rack gear of the straight bevel gear system is integrally formed with an outer peripheral face of the upper end of the ball discharge tube, and the rack gear is mutual-meshed with a drive gear of the straight bevel gear system, wherein the drive gear is coupled to a rotation shaft from a swing motor installed in the housing. a play field defined by a half line, both opposing end lines, and both opposing side lines, wherein the play field has a net extending along the half line; a vertical column structure adjacent to at least one of the end and side lines; and a ball supply apparatus coupled to the column structure at an upper portion thereof, wherein the ball supply apparatus includes: a housing coupled to the upper portion of the column structure, wherein a top portion of housing is partially open, wherein the housing is divided by a partition into a ball storage portion and a ball discharge portion, wherein a bottom face of the ball storage portion is inclined downward toward the ball discharge portion, wherein a first opening is formed in a bottom of the ball discharge portion, and a second opening is formed in the partition at a lower portion thereof; a rotatable opening/closing plate rotatably coupled to the partition, wherein the rotatable opening/closing plate is configured to rotate to open/close the second opening; and a ball discharge tube rotatably coupled to the ball discharge portion at the first opening, wherein the ball discharge tube ball-communicates with the ball discharge portion via the first opening, characterized in that the upper end of the discharge tube is inserted into the ball discharge portion through the first opening, wherein a straight bevel gear system is disposed in the housing, wherein a rack gear of the straight bevel gear system is integrally formed with an outer peripheral face of the upper end of the ball discharge tube, and the rack gear is mutual-meshed with a drive gear of the straight bevel gear system, wherein the drive gear is coupled to a rotation shaft from a swing motor installed in the housing. a housing coupled to the upper portion of the column structure, wherein a top portion of housing is partially open, wherein the housing is divided by a partition into a ball storage portion and a ball discharge portion, wherein a bottom face of the ball storage portion is inclined downward toward the ball discharge portion, wherein a first opening is formed in a bottom of the ball discharge portion, and a second opening is formed in the partition at a lower portion thereof; a rotatable opening/closing plate rotatably coupled to the partition, wherein the rotatable opening/closing plate is configured to rotate to open/close the second opening; and a ball discharge tube rotatably coupled to the ball discharge portion at the first opening, wherein the ball discharge tube ball-communicates with the ball discharge portion via the first opening, characterized in that the upper end of the discharge tube is inserted into the ball discharge portion through the first opening, wherein a straight bevel gear system is disposed in the housing, wherein a rack gear of the straight bevel gear system is integrally formed with an outer peripheral face of the upper end of the ball discharge tube, and the rack gear is mutual-meshed with a drive gear of the straight bevel gear system, wherein the drive gear is coupled to a rotation shaft from a swing motor installed in the housing.