Clue: Utter rallying cry from 1926? (3-3)
Answer: ALL OUT
Explanation: Definition: Utter rallying cry from 1926
*In 1926, the "General Strike" (19,26) took place, and "All Out" is what a shop steward would typically shout at the beginning of a strike. Also, as pointed out by minty in the comments, UTTER and ALL OUT are synonyms, so this is actually a double definition.