The American Legion donated $35,000 to the building of the stadium in 1964 with two stipulations. The new field would be named "Legion Field" and that a room at the field be provided free of charge to Legion members for meetings. There is an article in the Kingsport Times dated 08-27-1966 that talks about how the field came to be and the financing behind it.
As for Blue Devils. Like most early schools it was derived from the color of the uniforms. They wore blue so it looked like "Blue Devils" running around. This is true for many other schools such as Marion, Richlands, Grundy, Narrows, Wytheville and Galax. Just a variation on what they looked like such as "Hurricane", "Devils", "Waves", etc.