Springfield's Angry Mob is a recurring group throughout the Simpsons series, consisting of many of the townspeople of Springfield and usual secondary characters (including Abe Simpson and excluding The Flanders). They would often go after the Simpson family or at least another certain character on any given occasion.
They were after the Simpson family (although they originally only wanted Homer) because Homer polluted the lake by dumping a silo full of pig droppings (and some of his own), which caused the lake to get even worse with contamination than from the Green Day incident and prompted the EPA to put a city-sized dome over Springfield. Every citizen in Springfield (Including Abe Simpson; except The Flanders) were in the mob holding torches, pitchforks, guns and bows with arrows, and other weapons. Colin was also in the mob holding a bunch of flowers, but Carl turned it into a torch. When they were first seen, they were walking the wrong way but turned round when Homer shouted out his sardonic comments, alerting the mob of his position. The Simpsons were briefly captured by the murderous mob, but they eventually escape through the sandpit and are forced to escape Springfield.