Four-Point Contact Ball Bearings (FPCBB) typically exhibit 2- or 3-point contact under pure axial external loads and shaft-driven conditions. When the transition between contact states is considered as the critical contact state, these bearings display a distinctive critical contact effect. In this paper, a novel quasi-static model for FPCBB is proposed, which calculates friction with sliding velocity instead of raceway control hypothesis. On this basis, the critical contact effect of FPCBB is analyzed in detail, including significant changes in stiffness and suppression of ball motion. Furthermore, the critical contact effect is optimized by adjusting three structural parameters: arching dimension, initial contact angle, and groove curvature. This study provides valuable theoretical insights for the practical application and design development of FPCBB.