“We just have to stay alive,” Ms. Barnabas said of the main idea behind the Jarva District Patrol Competition, a 24-hour test of the skills useful for partisans, or insurgents, to fight an occupying army, and an improbably popular form of what is called “military sport” in Estonia.

The competitions, held nearly every weekend, are called war games, but are not intended as fun. The Estonian Defense League, which organizes the events, requires its 25,400 volunteers to turn out occasionally for weekend training sessions that have taken on a serious hue since Russia’s incursions in Ukraine two years ago raised fears of a similar thrust by Moscow into the Baltic States.

Estonia, a NATO member with a population of 1.3 million people and a standing army of about 6,000, would not stand a chance in a conventional war with Russia. But two armies fighting on an open field is not Estonia’s plan, and was not even before Donald J. Trump, the Republican presidential candidate, said European members of NATO should not count on American support unless they pay more alliance costs.

Since the Ukraine war, Estonia has stepped up training for members of the Estonian Defense League, teaching them how to become insurgents, right down to the making of improvised explosive devices, or I.E.D.s, the weapons that plagued the American military in Iraq and Afghanistan. Another response to tensions with Russia is the expansion of a program encouraging Estonians to keep firearms in their homes.