have a tight grip on (someone or something)

To maintain strict or tight control over someone or something; to not allow someone or something very much independence or autonomy. Ever since George lost most of their life savings in a drunken poker match, Dana has had a tight grip on the family finances. The boss has had a tight grip on her assistant ever since she first hired him. A: "Things seem tense in down in their department." B: "Yeah, I hear their new manager has a tight grip on everyone."