A model with this special rule must make a Special Attack in the Close Combat Phase at Initiative 0 against a single enemy unit in base contact, provided that the Troop Type of the target unit is Infantry, War Beast, Swarm or War Machine. This attack deals a number of hits equal to the value stated within brackets (X), which automatically hit and have a Strength equal to the model's own Strength. Hits caused by Stomp can only be allocated onto models with Infantry, War Beast, Swarm or War Machine Troop Type (ignore models of different Troop Type when distributing hits).
In multipart models, riders can never Stomp. Stomp attacks can only ever be allocated to models that can normally be stomped. Being a Special Attack, Stomp never benefits from any equipment or special rule the model has.