The mechanical model of the critical shear crack theory (CSCT) has been used in the past to investigate a number of shear-related problems, such as punching of slab–column connections with and without transverse reinforcement. In this paper, a discussion on the differences and analogies between slender slabs and squat members (footings) without transverse reinforcement is presented on the basis of the CSCT. This discussion highlights how bending and shear deformations influence the opening of the critical shear crack and eventually its ability to transfer shear forces. On that basis, it is investigated and justified a power-law expression to characterize the failure criterion of the CSCT. This criterion, in combination with a suitable load–deformation relationship, can be used to derive closed-form expressions for punching shear design. The accuracy of these expressions is verified against databases of slender slabs (121 specimens) and footings (34 specimens) with consistent agreement.