Eleven people were killed and at least 80 others were injured in clashes and police firing in three districts of Rajasthan during an agitation by the Gurjar community demanding ST status for themselves. The Army is out on the Jaipur-Agra national highway and Armymen were staging flag marches in several stretches along the road
Please explain the highlighed ones.
"a flag march" appears to mean that the Army is metaphorically "showing the flag" - showing that they are present, and ready to take action, by marching through an area where there is/has been trouble.
A stretch of road - a length of road