How does the Tholian Web trap a ship?

How does the Tholian Web work?

Energy filaments enclose a vessel, and the sealed web becomes self-generating, preventing escape and obstructing outgoing fire.

Energy filaments are woven around a vessel, and the completed web becomes self-generating. A ship trying to leave would be shredded by the filaments. Weapons can fire inward but cannot fire outward in this account. Offensive and defensive uses depend on how the web is woven, with differing descriptions of those roles.