Athletic Club II

Agustín Gaínza took charge in 1964, when Athletic Club revived an old name — Bilbao Athletic had existed briefly in 1938 — to build a proper reserve side.

What the side became is best measured by who passed through it. José Ángel Iribar and Julen Guerrero went up that way; so, decades later, did Iñaki and Nico Williams. Kepa Arrizabalaga and Unai Simón both kept goal here before doing it elsewhere and, in Simón's case, upstairs at San Mamés.

The shirts are the red and white stripes of the senior team, with black shorts.

The league record is a ladder climbed and slipped down more than once. The side took the Segunda División B title in 1982–83 and again in 1988–89, and in 2015–16 reached the second tier itself, where it finished bottom. Relegation to the fourth tier came in 2023. It lasted one season: the Segunda Federación title in 2023–24 sent the team straight back up to the Primera Federación.

Matches against Real Sociedad B carry the name Derbi Vasco de filiales.

Sixty years after Gaínza's appointment, the ground where all of this happens seats 3,250.