The Polish forces outside Moscow under the command of Jan Piotr Sapieha clash with the growing anti-Polish Russian forces of the so called First Volunteer Army, led by Prokopy Petrovich Lyapunov.

Prokopy and his brother Zakhary, Russians of Rurikid stock, had sided with False Dmitriy I after the death of Boris Godunov.

Prokopy in early 1606, had taken part in the Bolotnikov Uprising on the side of the rebels.

Lyapunov had come to Moscow in November of 1606 and given himself up to Vasili IV.

After his repentance, Lyapunov had been made a dvoryanin (noble) of the Boyar Duma (1607).

Lyapunov had in 1608–1610 led the army of service class people against a peasant uprising in the Ryazan region and supporters of False Dmitriy II.

Lyapunov had been the one to organize the overthrowing of Vasili IV in July of 1610.

When the Polish army occupied Moscow, Lyapunov, inspired by Patriarch Germogen's proclamations, had levied the so-called First People's Volunteer Army and become its leader.

The People's Volunteer Army approaches Moscow in March of 1611 and blocks the Polish invaders.