The opposite of "gives some slack" can be "holds tight", "sticks rigidly", or "enforces strictly". When one "gives some slack," they allow some room for flexibility or leniency in a situation. However, if one "holds tight," they refuse to yield and maintain a strict approach. Similarly, if one "sticks rigidly," they refuse to modify their position despite any circumstances. "Enforcing strictly" involves not allowing any deviation from rules or guidelines. In essence, the opposite of "gives some slack" pertains to sticking to a rulebook, where the rules are applied without any bending or flexibility, and no exceptions are made.