The ability to control the plastic deformation of amorphous metals is based on the capacity to influence
the percolation of the shear transformation zones (STZs). Here, by using molecular dynamics simulations, we provide a unique atomic-level mechanism underlying the STZ percolation process. The mechanism is based on the autocatalytic generation of successive strong strain (STZ) and rotation fields (vortex-like motion), leading to STZ percolation and, ultimately, to the formation of a shear band. Through the proper control of the STZ-vortex sequence, one could handle the shear band dynamics and avoid runaway instability, thereby improving the plastic deformability of metallic glasses at room temperature. These findings may have significant implications for understanding several aspects characterizing the process of shear banding in metallic glasses and other disordered materials.