Rigid barriers are commonly used as defense measures in hilly areas to contain falling boulders and landslide debris, and the sliding displacement of these barriers is a key design consideration when space is limited. A new displacement-based model in the form of a closed-form solution is introduced in this paper to estimate the amount of sliding displacement that a barrier undergoes following a boulder impact. The model was derived based on the principles of energy and momentum conservation, and the derivations were presented. Laboratory tests were conducted to validate the analytical model, and the results consistently matched the analytical results for different impact velocities. Finite-element modeling was subsequently carried out on a real-scale barrier in Hong Kong to verify the scale-independent nature of the model. A parametric study was also carried out to investigate the effect of basal friction on the sliding behavior of the barrier. The results revealed that the effect of friction diminishes with increasing barrier:boulder mass ratio.