According to the Polish mass media, the reason for the protest was the ban on carrying a provocative banner with the inscription: We remember Volyn.
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Ultras believe that this inscription does not contain prohibited symbols, but the security service of the Donetsk club did not allow the banner to be carried.
After that, the Polish fans declared that they would not go to the stands without this banner and stayed outside the arena.

PHOTO by Sport.ua. Legia fans refused to enter the stands of the match against Shakhtar
Source: sport.ua