[1][2] He was one of the co-founders of Athletic Club in 1901 and was part of the team that won the 1902 Copa de la Coronación, the first national championship disputed in Spain.
[5] Larrañaga soon made his debut, thus becoming the club's first-ever player from the Enkarterri district (which today is defined as the more rural part of western Biscay but then included Portugalete and other industrial towns closer to Bilbao, referred to collectively as the left bank).
[6] In 1902, Larrañaga played a few friendly matches against city rivals Bilbao Football Club in the Hippodrome of Lamiako,[7] including the first paid match held in Biscay on 19 January 1902 (probably his debut), in which the newspapers of the time reported that "Larrañaga, as always, was a very reliable defender who did not leave his position for a moment".
[12] In 13 March 1904, he played for Athletic de Portugalete in a friendly against Athletic de Bilbao, keeping a clean sheet in a 0–0 draw,[3] and was therefore invited to play for the Bilbao club again; he was listed in the team that won the 1904 Copa del Rey without playing a single match, since their opponents failed to turn up,[13][14] and later that year he was in the first-ever line-up that faced Madrid FC (now Real Madrid CF) on 24 April 1904, his side winning 2–1.
[17] In 2013, the Encartaciones Museum, in the Avellaneda Meeting House, in Sopuerta, held a temporary exhibition that compiles the connection between this Biscayan region and the Left Bank with Athletic in the last century, and Larrañaga received special attention as the club's first-ever Encartado.