La Liga leaders Barcelona fell to a 1-0 defeat at Real Sociedad on Sunday as they had a Robert Lewandowski goal controversially disallowed. Sheraldo Becker’s 33rd-minute goal consigned the Catalan giants to their second league defeat of the season, leaving Hansi Flick’s side six points clear of second-placed Real Madrid, having played an extra match. Lewandowski’s early disallowed strike led to furious debate over whether the Polish forward had been offside or not. Barcelona were without teenage star Lamine Yamal after he suffered a blow to his ankle in the Champions League win at Red Star Belgrade midweek and badly missed his spark. The Catalans failed to score in a match for the first time this season across all competitions as Real Sociedad, eighth, held firm, while Barcelona did not manage a single shot on target. “It’s a tough place to go, where La Real push a lot… we have to learn from our mistakes and that’s it,” Barcelona midfielder Pedri told Movistar. “Normally we score goals but today we weren’t accurate, I think it will be a one-off, and in the following games we we’ll be more precise. “I think the team is working well and (not scoring) is not something that worries me.” Playmaker Dani Olmo started on the bench while defender Pau Cubarsi played in a mask after suffering a cut which needed stitches on his face in Serbia. The Catalans have struggled in San Sebastian in the past and were given another uncomfortable night in the Basque country. Lewandowski thought he had fired Barcelona in front after 13 minutes when he reacted well to a blocked shot to fire home, but the goal was ruled out following a VAR review. Referee Guillermo Cuadra Fernandez was told Lewandowski was offside, although the forward did not appear to be in front of Real Sociedad defender Nayef Aguerd. The semi-automated offside technology used in La Liga indicated the front of Lewandowski’s boot was off, but Spanish media furiously debated whether the technology had misinterpreted Aguerd’s heel as part of the veteran striker’s boot.