This made him the club's second-youngest debutant (behind Domingo Acedo in 1914), a statistic which lasted until 2009 when Iker Muniain surpassed the appearance record by seven days[1] and equalled the scoring one the following week.
[9] Gainza also set several Spanish Cup records: he won seven editions, appeared in nine finals, played most for one club in the competition (99 games),[4][10] and was the highest scorer in a single match, having claimed eight goals in a 12–1 victory over Celta de Vigo in the 1947 quarter-finals after a 1–0 loss in the first leg.
He made his debut on 11 March 1945 in a friendly against Portugal and, as with Athletic, was team captain in the 1950 FIFA World Cup as the country finished in fourth position.
[13][14] It was reported that as a child Agustín was not interested in football and had to be encouraged to play the game by Miguel,[3] and even when approached by Athletic in his teens was reluctant to take it up as a career, with his brother persuading him to agree terms.
One was displayed outside his family home in Basauri (having been donated to the town by the local supporters' club),[15] and the other was situated at the Athletic Bilbao training headquarters at Lezama.