Groffgut's Gang was a group of young water rats that originally lived south of Redwall Abbey along with other vermin bands. Groffgut's band was smaller and younger than the other bands, so they were often the butt of jokes. Groffgut decided to wander north so that the gang could prove themselves.
When a wounded Pandion Piketalon crash-landed in Mossflower Woods, the gang captured the osprey and tortured him, intending to eat him after they had had their fun. Fortunately for Pandion but unfortunately for the rats, they were seen by the Redwall squirrel Girry; he and his friends Tiria Wildlough the otter, Brinty the mouse, and Tribsy the mole immediately set about attacking the gang and rescuing the osprey. Brinty gave Groffgut a savage beating, for which the water rat swore revenge. In an attempt to bring this about, the gang marched along the path towards Redwall the next day. Tiria saw them and shot Hangpaw, killing him and causing the others to flee. Skipper Banjon Wildlough pursued them, but they hid in a swamp until he was forced to give up the search and return home.
The gang later tried to enter Redwall Abbey one night by standing on top of each other's heads to climb over the wall, but they were spotted by Abbess Lycian and Burbee. The two Redwallers threw a pot of hot tea at the water rats, causing them to fall on top of each other. Plugtail, Threetooth, and Groffgut were injured in the process. The crew then decided to watch for another attempt to invade the Abbey.
Later, when Brinty was fighting a hungry gannet which had entered Redwall, he opened the gate and thrust the bird out. Groffgut, seizing the opportunity of the open gate, rushed out of his hiding place and slew the mouse; Banjon threw the Lance of Corriam Wildlough and killed Groffgut. The gannet attacked and killed Plugtail and Frogeye, and the other gangmembers fled, never to be seen near Redwall again.
Interestingly, Groffgut's gang is one of the very few vermin bands of which everybeast in the band is named (with the possible exception of Burrad's Band).
Groffgut's Gang appears in High Rhulain.