The actions of Athletic Bilbao fans are related to the fact that Barcelona have been accused of bribing referees in the past.

In the match on San Mames Stadium between Bilbao and Barca in the 25th round of La Liga in the morning of March 13 (Hanoi time), the fans of the home team threw a banknote with Barca’s logo printed with the words “Mafia” to mock the away team. The move comes as the Catalan club is being investigated over payments to former Vice President of the Technical Committee of Arbitration (CTA), Jose Maria Enriquez Negreira.
On March 11, prosecutors accused Negreira of receiving more than 7.3 million euros ($7.8 million) from Barca between 2001 and 2018. On the side of the Catalan club, former presidents Josep Maria Bartomeu and Sandro Rosell are accused of giving bribes. The club’s current president, Joan Laporta, denied the allegations and said Barca was not involved in the matter.
The Catalan club explained that it paid Mr. Negreira as a consultant, to provide reports related to the referees who control La Liga matches. But when he testified before the Prosecutor’s Office, Mr. Negreira was unable to produce any documents proving that he had provided these types of services to Barca.
Under Spanish law, individuals prosecuted can face up to four years in prison for individuals, or a ban from engaging in business activities. Barca club can be fined or banned from operating.
On the San Mames field, Barca still focused on playing and won 1-0 against Bilbao with Raphinha’s goal in the 45+1 minute. Coach Xavi’s teachers and students went down in La Liga history when they became the team with the best defensive record in La Liga after 25 matches when they only conceded 8 goals. The previous record belonged to Atletico Madrid in the 1990/91 season and Deportivo de La Coruna in 1993/94 (10 goals).
Winning Bilbao, the Catalan team re-established the 9-point gap with Real Madrid on the La Liga 2022/23 rankings.
Source: https://zingnews.vn/cdv-bilbao-nem-tien-gia-xuong-san-de-che-nhao-barca-post1411340.html