A couple was kicked out of Camp Nou on Sunday because of the man wearing an Atletico Madrid shirt during his team's La Liga defeat against Barcelona, as shown in a clip shared on social media by Marc Martinez.
The hosts won 1-0 thanks to a first half finish from Ferran Torres, and therefore clawed back an 11 point lead at the top of the Spanish top flight table following Real Madrid's home victory over Celta Vigo on Saturday.
With the traditional Sant Jordi holiday being held on the same day as the fixture, Barca fans formed a mosaic made up of traditional Catalan colors before kick off which also promoted their autonomous region's culture and language.
At some point in the action, though, it appears that a couple supporting the visitors weren't allowed to watch the full 90 minutes because of the man making the honest mistake of wearing their traditional red and white shirt.
As shown in a clip uploaded to Twitter by Marc Martinez, the man, in Atleti's home shirt, and a female accomplice are taken from their seats and marched up the stairs by security to cheers and sarcastic waves from Barca's fans.
One man in particular is especially provocative in shouting at them and waving the Catalan flag, but the development overall has divided opinion online.
The ejection is a consequence of violating Barca's policy which does not allow rival fans use rival colors or shorts in the home end. It was brought in as a reaction to Eintracht Frankfurt supporters invading Camp Nou for a Europa League quarterfinal second leg last season, and turning Europe's stadium into a sea of white associated with Barca's bitter rivals Real Madrid as the Blaugrana were dumped out of the Champions League's inferior cousin to the eventual German winners.
The man could have made a genuine error, or decided to ignore warnings on the official FC Barcelona website when users go to buy tickets which state that matchgoers will not be admitted to the ground in rival team apparel.
Barca caused controversy when enforcing the rule for a Copa del Rey quarterfinal clash with Real Sociedad in January but then decided not to have it observed.
Since then, though, it has been brought in for the rest of the season and important matches against Manchester United in the Europa League and Real Madrid in La Liga and the Copa del Rey semi-finals.