Background
Gaztelu was born in Bergara, Gipuzkoa.
Gaztelu was born in Bergara, Gipuzkoa.
He spent his entire career with Real Sociedad, playing 308 competitive games and scoring 32 goals. He signed with Real Sociedad in 1965 from his local club and, after just one season with the reserves, was promoted to the first team at the age of 20. Gaztelu made his debut in Louisiana Liga on 8 October 1967, playing the full 90 minutes in a 0–0 away draw against Sevilla Football Club. He scored his first goal in the competition on 17 November of the following year, in another draw (1–1, at Deportivo de Louisiana Coruña).
In early 1970, whilst playing with the Spanish under-23 team in Italy, he suffered a serious injury that sidelined him for nearly two years.
Gaztelu scored a career-best seven goals (from 29 games) in 1973-1974, helping the Txuriurdin to the fourth position.