A crackdown (one word, no hyphen) is an official effort to forcefully repress or restrain something. Crack down (two words) is crackdown‘s corresponding verb. To crack down is to forcefully repress or restrain. For example, repressive governments tend to crack down on antigovernment protests. The actions these governments take against the protests might be termed crackdowns. Crackdowns tend to be especially harsh, usually involving force.