Basel continued their dominance of Swiss football by winning their fifth successive league title with a 3-1 win away to Aarau on Thursday.
An 8,000 crowd packed into Aarau's tiny ground and the game ended in chaos when Basel fans staged a pitch invasion after the final whistle.
Television pictures showed Basel fans, many of them hooded, clashing with riot police and throwing objects at the home fans, although the situation was quickly brought under control.
The win gave Basel an unassailable four-point lead over Grasshoppers, who beat Luzern 4-1, with one match each to play.
Basel qualified directly for next year's Champions League group stage while Grasshoppers, who have made sure of second place, will go into the third qualifying round.
Congolese defender Igor Nganga gave Aarau a sixth-minute lead when he turned the ball in from close range, but Ivorian Serey Die equalised in the 28th minute with a low 25-metre shot which went through a crowded penalty area and caught goalkeeper Lars Unnerstall unsighted.
Argentine midfielder Matias Delgado gave the visitors the lead five minutes later, curling in a 25-metre free kick, and Valentin Stocker sealed the win with 11 minutes to play.
Basel have won a total of 17 league titles, still 10 short of Grasshoppers' record of 27.