Abstract: Asymmetric sudden damage of the roadside backfill is a core bottleneck restricting gob−side entry retaining in deep, high−stress, and soft−rock mining. To reveal its catastrophic triggers, taking the 12301 deep−buried and strong−rheological working face as the engineering prototype, this study systematically elucidates the eccentric loading drive effect and joint instability mechanism of overlying key block rotation on the backfill wall through integrated theoretical analysis, numerical simulation, and field monitoring. The results indicate that the asymmetric rotation of overlying key blocks induces severe eccentric compression at the top of the backfill and generates a shear−tensile composite stress concentration zone internally, driving a progressive asymmetric damage evolution from the gob side to the entry side. Once the rotation angle reaches a critical threshold, the coalescence of the plastic zone triggers structural plane slip instability. Consequently, a synergistic control strategy involving "asymmetric differential high−toughness grouting" and "flexible energy−absorbing roof cutting" is proposed. Field engineering trials demonstrate that the optimized backfill deformation is reduced by 45%, effectively suppressing eccentric damage. The research findings clarify the mechanical linkage between deep strata movement and side−support response, providing theoretical guidance for surrounding rock control in deep gob−side entry retaining.