Police fired rubber bullets at rioting crowds after celebrations of Barcelona's league title spilled over into violence.
Police said yesterday that 65 people were arrested overnight, while 51 suffered minor injuries in the disturbances.
About 15,000 raucous supporters had gathered at the city's Canaletes fountain on Las Ramblas avenue, the traditional site for celebrating the Catalan club's title wins.
A few hours into the celebrations, a group of around 100 people at nearby Plaza Catalunya started launching bottles and other projectiles at the police. That led to plain-clothed officers making arrests, which provoked further trouble.
Following police warnings, officers charged at the crowd and fired rubber bullets. The arrests were made for vandalism, public disorder and resisting authority, police said.
Barcelona secured the Spanish league title on Saturday after its closest rival Real Madrid lost 2-3 at Villarreal, providing the Catalan team with an unassailable eight-point lead in the standings.
In comments published on the club's Website, Barcelona President Joan Laporta had expressed his wish for fans to celebrate the team's second trophy of the week "quietly and calmly".
Barcelona won the Copa del Rey last Wednesday to complete its first domestic double for 11 years. The team also has the chance to win the Champions League on May 27 when it plays defending champion Manchester United in Rome.
Third straight defeat
Robert Pires, Ruben "Cani" Gracia and Joan Capdevila scored for Villarreal to condemn Real to its third straight defeat and leave the team to suffer its first trophyless season since 2005-06. Rafael van der Vaart and Gonzalo Higuain replied for last season's champion.
"The league is the fairest competition and a test of consistency and I think Barcelona deserved to win it," Real coach Juande Ramos said.
Barcelona, which was at Mallorca yesterday, has 86 points with three games left, while Real has 78 with two to play.
The 19th title in Barcelona's history was a triumph for 38-year-old coach Pep Guardiola, the club's former midfielder who was in his first season in charge.
"They have had a magnificent season, one of the best in Barcelona's history. I am convinced they can achieve even more this season, for example, the league record of 107 goals," Laporta said.
Barca has scored 103.
Villarreal's victory lifted it to fifth place with 59 points, level with Valencia.
Also on Saturday, third-place Sevilla remained on course for a place in next season's Champions League despite being held to 0-0 by lowly Osasuna.
With two matches to play, Sevilla has 64 points and was five points clear of Valencia, which was at Atletico Madrid.
(Agencies via Shanghai Daily May 19, 2009)
