What is it that usually happens when you want to get some work done in a government office? You ask a clerk something and he grumpily tells you that you have to go to some other department; when you go there, you are told you are in the wrong place. You are constantly given the runaround. When you run from pillar to post, you are constantly on the move; you are made to go from one place to another, but you don’t achieve anything at all. There is a lot of aimless running around. The idiom carries with it the sense of being harassed. The expression has been around for several centuries, and when it entered the language it was “from post to pillar”.
*The students were made to run from pillar to post for their mark sheet.
According to some scholars, the expression comes from the world of court tennis — a game that I understand is very different from the game of lawn tennis that is played today. Another theory is that the expression refers to a form of punishment that was meted out to criminals. In the old days, criminals were first tied to a “post” in the marketplace and whipped. After that they were dragged to a pillory (“pillar”). This was essentially a wooden frame that had three holes in it. The prisoner was made to put his head and his two hands through the holes, and made to stand or kneel for days together. The public had fun throwing rotten vegetables and eggs at the hapless victim.