The present work addresses the evaluation by numerical simulation of the extreme loads acting on a flap-type wave energy converter. To this aim, a realistic situation is considered: an extreme wave impacting a bottom-mounted pitching device, consisting of a partly submerged flap, placed in front of a dike on the coast of Bayonne, south-west Atlantic coast, France. The SPH model can be an optimal candidate for this kind of study: its Lagrangian character allows for an accurate description of the extreme breaking wave acting on the structure, while its meshless feature permits an easy interaction of the fluid with moving rigid bodies such as the rotating flap converter. An analysis of the influence of different environmental conditions (tide level, wave breaking occurrence) on the load intensity is performed. Several impact dynamics are studied and it is found that, in some specific conditions, the process develops in a sort of “flip through” impact, similarly to what observed for wave impact on rigid walls. The most critical cases have been also reproduced with a fully 3D SPH model, highlighting the greater complexity of the flow and the limits of the 2D modeling.