This paper provides a rigorous academic systematization of Mindung Ssireum (traditional Korean free-grip standing wrestling), specifically analyzing its biomechanical traits, grip mechanics, and its structural position within the holistic combat system of Subak. Based on historical audiovisual data from the 1930s–1940s in Northern Korea and consistent oral histories from lineage practitioners (e.g., Grandmaster Song Chang-ryeol), this study corrects prevailing misconceptions that Mindung Ssireum is merely a beltless variation of modern sports Ssireum. Biomechanical analysis reveals that Mindung Ssireum operates through everyday clothing grips, aggressive neck-wrapping (clinch), and forward bodyweight pressure, utilizing leg hooks strictly as a secondary mechanism. Crucially, this paper establishes that when evaluated under strict historical protocols, Mindung Ssireum concludes upon achieving a standing takedown and ground control, explicitly excluding ground striking or mounting. Instead, the full mount and subsequent striking are defined as the definitive finishing mechanisms unique to Subak, cementing Mindung Ssireum as the structural transitionary bridge within the overarching Subak martial lineage.