We examine the mechanics of shear deformation, rupture and frictional sliding of fiber coatings in ceramic composites through a combination of experiments, modeling and computational simulations. The work includes fiber push-in tests in several prototypical SiC-SiC composites with BN coatings on the fibers, using an established model of brittle interface fracture and subsequent sliding to interpret the data. The test results reveal two distinct behaviors: one in which a crack appears to form suddenly within the coating or at one of the interfaces with neighboring phases, followed by interface sliding (in accord with the established model), and another in which yielding of the BN occurs first, followed by rupture and sliding. Deficiencies in the existing brittle interface model are addressed through extensions of the model that account for coating plasticity prior to rupture. An analytical model based on shear lag analysis is developed and validated by finite element calculations and subsequently used in the interpretation of the test data. The work provides a new framework for interpreting fiber push-in results, including ways to ascertain the mechanism that governs the stress for push-in initiation and for extracting pertinent coating properties. It also highlights the important role of plasticity in the design and performance of fiber coatings for ceramic composites.