Here’s a clear postcard showing the Chester Nebraska school in the mid-50s.  The card also mentions that it is the “Home of Six Man Foot Ball”.

From Wikipedia: Six-man football was developed in 1934 by Stephen Epler in Chester, Nebraska, as an alternative means for small high schools to field a football team during the Great Depression. The first game was played on Thursday, September 27, 1934, at the Hebron, Nebraska Athletic Gridiron, under the lights, with a crowd of almost 1000 watching. This game was played so that coaches all over Kansas and Nebraska could see if they wanted to try this new game of six-man. The two teams playing in the game were the combined team from Hardy-Chester (“Hard-Chests”) and a combined team from Belvidere–Alexandria (“Belvalex”). The two teams had two weeks to practice prior to this game; the two teams played to a 19-19 tie.^[1] After that night, rules for the game were distributed to about 60,000 coaches in the United States.^[2]