Legia went 2-0 up in the second half thanks to goals from Domagoj Antolic and Michal Kucharczyk, causing home fans to invade the pitch and throw flares before they were chased away by riot police. The referee was left with little option but to take the players off the pitch with just 13 minutes to go, with the Polish Ekstraklasa later granting Legia a walkover.
A statement read: "As a result of this decision Legia Warsaw has 70 points and the title of Polish champion is assured. Lech Poznan has 60 points and third place on the podium."
The triumph was Legia's third consecutive Polish league title, whilst Poznan will face a separate disciplinary hearing on Thursday to discover what action they will face.
Jagiellonia finished the season as runners-up after they won their final game of the season 2-1.