Mauhur commanded a group of Isendgarder Orcs
in the forest to aid Ugluk on his return. This may have been originally
to help them wrest the hobbits from the Mordor Orcs, but were instead
to fight against the Rohirrim. The riders were too much and were well
to handle even the reinforced Orcs, killing most of them.
Reference: The Two Towers: "The Uruk-hai"