Multiaxial deformation of Zr55Al10Ni5Cu30 metallic glass was investigated by instrumented indentation tests with a spherical indenter. Contrary to the elastic–rigid-plastic behavior of bulk metallic glasses (BMGs), indentation pressure showed a significant increase with increasing indentation strain, and it was ascribed to a rapid transition of the plastic constraint factor (PCF). However, it was impossible to measure the PCF values from the indentation pressures in the Zr-based BMG because information on uniaxial flow stress was insufficient due to the limited flow strain of 2.2%. Here we developed a PCF assessment method using a relative residual depth hf/hmax, which was experimentally confirmed by adopting it to spherical indentations of a steel sample having well-known flow properties. Flow properties of the BMG were calculated using the new PCF assessment method, and the effects of the materials pileup and low strain indentations on PCF and flow properties were discussed.