VIDEO: Flare thrown at Boston United fans
It should have been an afternoon to remember for both sets as supporters as the Ammies clinched the National League North title while the Pilgrims moved to within four points of the play-offs.
But one person in the crowd had other ideas.
After evading one steward he ran to the away end, throwing the flare towards Pilgrims supporters, narrowly missing them as it struck an advertising hoarding.
United players and fans remonstrated with the man, dressed in dark clothing and wearing a cap, before stewards got hold of him.
However, he was allowed to leave the stadium seconds later.