Nobody expected that result, but it should be noted that this is the second game without Yamal in the lineup and the second defeat of Barcelona, apparently the dependence on Yamal is very serious, if without him Barcelona can not score and moreover, Barcelona has not been able to score a single shot on goal Real Sociedad, which is strange for the leader of La Liga.
There was also a controversial decision of VAR when they canceled the clean goal of Lewandowski, because the picture shows that the foot of the Real Sociedad defender was offside, so the referee's mistake seems to have helped Real Sociedad to win.
Many of us are surprised by this result which we know on paper Barcelona is far superior to its opponent especially in this season they are very consistent many strong teams have become victims but when playing against Real Sociedad Barcelona seemed helpless I do not understand what the reason behind the defeat but maybe as you said Yamal's absence the attack built by Barcelona was not so effective as proven from 11 shots none of them hit the target, the only best chance was a goal that was disallowed by the referee. And not only you I also question the controversial decision.