'Obstruct' is Latin for 'build against' — the vivid image of someone walling off your path.
To block or impede passage, progress, or action; to deliberately hinder or prevent.
From Latin 'obstruere' (to block up, to build against, to barricade), composed of 'ob-' (against, in front of, toward) + 'struere' (to pile up, to build, to arrange in layers), from PIE *strew- (to spread, to strew, to scatter in a layer). The root *strew- generated a productive building-and-spreading family: Latin 'struere' (source of 'construct', 'destroy', 'instruct', 'structure'), Old English 'streowian' (to strew — ancestor of English 'strew'), and Sanskrit 'stṛṇāti' (he strews). The original Latin 'obstruere' had a concrete sense of physically blocking a passage by piling
The legal charge 'obstruction of justice' literally means 'building a wall against justice' — the same metaphor the Romans used when 'obstruere' described building a barricade across a road. The political tactic of 'obstructionism' (using procedural maneuvers to block legislation) and the medical term 'bowel obstruction' (a physical blockage) both preserve the ancient image of something piled up in the way.