|Full name||Agustín Guisasola Zabala|
|Date of birth||22 July 1952|
|Place of birth||Eibar, Spain|
|Height||1.82 m (5 ft 11 1⁄2 in)|
|* Senior club appearances and goals counted for the domestic league only.
Born in Eibar, Gipuzkoa, Guisasola made his senior debuts with local SD Eibar at the age of 17, going on to play one-and-a-half seasons in Tercera División there. In late January 1971 he was bought by Basque giants Athletic Bilbao, making his official debut on the 31st in a 2–0 La Liga home win against Celta de Vigo, with his team eventually finishing fifth and qualifying for the UEFA Cup.
Midway through the 1971–72 campaign, manager Ronnie Allen was fired, but Guisasola was by now an essential defensive unit for Athletic. During his spell with the club he started as a full back, moved to central defender, was also deployed as a defensive midfielder and finished again in the defensive wings; in two consecutive seasons under Milorad Pavić he scored ten league goals combined, with Bilbao also winning the 1973 edition of the Copa del Rey.
In 1975–76, Guisasola played very little under manager Rafael Iriondo, who also tried to reconvert him in to forward. He regained his importance after the coach's departure, helping Athletic to two finals in 1977 (both lost, the UEFA Cup against Juventus FC and the domestic cup against Real Betis) and being named by L'Équipe Europe's best stopper.
During the better part of his career, Guisasola struggled with weight problems, and his production was highly inconsistent in his final years. An injury to starter José Ramón Alexanko – later of FC Barcelona fame – propelled him to the starting XI once again, and he helped Athletic finish seventh in the 1979–80 season; as they won the league in 1983, under Javier Clemente, he only contributed with four games (151 minutes).
Guisasola retired in May 1983 at almost 31, having appeared in 334 official games for Athletic Bilbao, with neighbouring Real Sociedad being invited to his testimonial match. Subsequently, he lost all connection to the football world.
- Athletic Bilbao
- "Los cachorros son casi leones" [The pups are almost lions] (PDF) (in Spanish). Mundo Deportivo. 23 May 1975. Retrieved 7 December 2015.
- "Un defensa con toda la barba" [Full-bearded defender] (in Spanish). Gara. 17 June 2013. Retrieved 6 April 2017.
- El campeón de Liga, hoy en el Manzanares (The League champion, today at Manzanares); El País, 1 June 1983 (in Spanish)