premise: Club Atlético Unión de Mar del Plata is an Argentine sports club from Mar del Plata, Buenos Aires Province. The club was founded on December 1, 1926, and its main sports are football and basketball. In football, Unión currently plays in the Torneo Argentino A, which is the regionalised third division of the Argentine football league system.
hypothesis: Club Atlético Unión de Mar del Plata has been playing basketball since 1926.
reason: 1926 is when the club was founded, but it's not mentioned what sports they played at the time. I think this confused the system because most of the context focuses on football, even though the club does play other sports (with basketball specifically mentioned).