To trammel is to hamper or hinder — in other words, to keep someone from doing something. People in your neighborhood might lobby for speed bumps in order to trammel speeding cars.
When you use trammel as a verb, you're either talking about limiting or catching, like when a fisherman trammels cod in a net. As a noun, a trammel is some kind of restraint. There's the trammel that's used by horse trainers to restrain a horse and slow its gait, and the trammel that's basically a fishing net. The latter is the original meaning of trammel, from the Latin roots tri-, "three," and macula, "mesh."