The term 'Sudden Restriction on Activity' can be summarized by the word 'CLAMPDOWN', which is a nine-letter word. A CLAMPDOWN is an abrupt and strict enforcement of rules or regulations, usually in response to a perceived problem or threat. It is often used to describe a government's response to a situation, such as a crime wave or civil unrest. Clampdowns are also used to enforce laws or regulations in other areas, such as business or industry.