player depth; pool of players
Used in sports to describe the overall quality and quantity of players available in a team, especially beyond the starting lineup.
This team has deep player depth, so it's okay even if someone gets injured.
To win the championship, a solid pool of players is essential.
Compound of 選手 (player) and 層 (layer, stratum). The term is a modern sports expression with no known historical derivation beyond the combination of its components.