The Skirmish in Cirith Ungol was a small conflict between Gorbag's and Shagrat's forces during the War of the Ring, albeit a very important one, as it allowed Frodo and Sam to escape from Cirith Ungol and continue their quest to destroy the One Ring.
After Frodo's unconscious body was brought to Cirith Ungol by Orcs for torturing and questioning, Gorbag and Shagrat began looting him. After finding his Mithril Vest, Gorbag wanted to keep it for himself, but Shagrat insisted that it be given to the Great Eye, most likely out of fear than loyalty. This lead to a skirmish between the Uruks and Orcs in the tower, leaving almost every one of them dead. Moments later, Sam sneaked into the tower, killed a few of the remiaiing Uruks, and saw Gorbag's failed killing attempt. He then rescued Frodo and they both escaped to continue their quest to Mount Doom.