controversialist, disputant, eristic - a person who disputes; who is good at or enjoys controversy

naysayer - someone with an aggressively negative attitude

stonewaller - one who stonewalls or refuses to answer or cooperate; someone who delays by lengthy speeches etc.

bar - an obstruction (usually metal) placed at the top of a goal; "it was an excellent kick but the ball hit the bar"

barrier - a structure or object that impedes free movement

blockade - prevents access or progress

blockage, stoppage, occlusion, closure, block, stop - an obstruction in a pipe or tube; "we had to call a plumber to clear out the blockage in the drainpipe"

hindrance, preventative, preventive, encumbrance, incumbrance, interference, hitch - any obstruction that impedes or is burdensome

obstacle - an obstruction that stands in the way (and must be removed or surmounted or circumvented)

structure, construction - a thing constructed; a complex construction or entity; "the structure consisted of a series of arches"; "she wore her hair in an amazing construction of whirls and ribbons"

tumbler - a movable obstruction in a lock that must be adjusted to a given position (as by a key) before the bolt can be thrown