To obstruct is to get in the way of, or stop something. An obstructionist is a person who is trying to obstruct something. An obstructionist stance is a position intended to obstruct.

Yes.

Obstruct.

To block up; to stop up or close, as a way or passage; to place an obstacle in, or fill with obstacles or impediments that prevent or hinder passing; as, to obstruct a street; to obstruct the channels of the body., To be, or come, in the way of; to hinder from passing; to stop; to impede; to retard; as, the bar in the harbor obstructs the passage of ships; clouds obstruct the light of the sun; unwise rules obstruct legislation.

The colonists placed palisade walls around their town to obstruct the natives from raiding them.