young baseball player; high-school baseball player
Refers specifically to a teenager who plays baseball, most commonly a high-school baseball player. Often used in the context of the national high-school baseball tournament (甲子園).
As a high-school baseball player, he is aiming for Koshien.
The young baseball players train hard every day.
high-school baseball player
Compound of 球 (ball, baseball) and 児 (child, youth). The exact historical derivation is uncertain, but the term is conventionally used for young baseball players.