Mother club, satellite club: how a 1903 Basque branch in Madrid became Atlético — and why both halves still wear the same red-and-white

On 26 April 1903 three Basque students living in Madrid registered a club they called Athletic Club Sucursal de Madrid — Athletic Club, Madrid Branch. It wasn't a founding in the usual sense. It was a satellite, a youth offshoot of Bilbao's Athletic Club, wearing the same blue-and-white halved shirts as the parent. That branch is now Atlético Madrid. The two clubs were formally affiliated until Atléti's independence in 1921; they switched together to red-and-white stripes around 1910, and both still wear them more than a century later because the lineage is the kit.