On 14 June 1925, in a spontaneous reaction against Primo de Rivera's dictatorship, the crowd in the stadium jeered the Royal March. As a reprisal, the ground was closed for six months and Gamper was forced to relinquish the presidency of the club. This coincided with the transition to professional football, and, in 1926, the directors of Barcelona publicly claimed, for the first time, to operate a professional football club. On 3 July 1927, the club held a second testimonial match for Paulino Alcántara, against the Spanish national team. To kick off the match, local journalist and pilot Josep Canudas dropped the ball onto the pitch from his airplane. In 1928, victory in the Spanish Cup was celebrated with a poem titled "Oda a Platko", which was written by a member of the Generation of '27, Rafael Alberti, inspired by the heroic performance of the Barcelona goalkeeper, Franz Platko. On 23 June 1929, Barcelona won the inaugural Spanish League. A year after winning the championship, on 30 July 1930, Gamper committed suicide after a period of depression brought on by personal and financial problems.

In 1925 what incident by the crowd caused the closing of the stadium?