Herri kirolak–traditional sports–are one of the defining features of Basque culture. Many of these sports developed out of everyday chores like chopping wood or lifting heavy objects. Neighbors would then challenge each other to informal feats of strength and/or stamina and out of these challenges, the custom of betting on the outcome developed. Nowadays these challenges take place in organized settings, typically during local fiestas for example, and involve formal, regulated competitions.
Check out the following short video from Iparralde that explains in brief form a gathering of competitors in various Basque sports in the town of Donapaleu (Saint-Palais) in Lower Navarre.
The Center has published books on several aspects of sports in Basque culture. See, for example, Basque Pelota: A Ritual, an Aesthetic by Olatz González Abrisketa, and Playing Fields: Power, Practice, and Passion in Sport, edited by Mariann Vaczi.