Definition by Wonder Me!: 
Pharmacologic antagonist binds the receptors. It doesn't make the receptor do anything. It just blocks the receptor from doing anything the receptor is supposed to be activated to do because the pharmacologic antagonists block the receptors preventing other agonists to bind to the receptors to activate the receptors to do anything.

Clinical example:
Propranolol (nonselective β1 and β2) 

Why it works?

"Beta blockers work by blocking the effects of the hormone epinephrine, also known as adrenaline. When you take beta blockers, the heart beats more slowly and with less force, thereby reducing blood pressure. Beta blockers also help blood vessels open up to improve blood flow." (1)

Citations:
(1)  http://www.mayoclinic.org/diseases-conditions/high-blood-pressure/in-depth/beta-blockers/art-20044522