As a player, have you taken a corner kick? Has a corner flag post every got in a way of your kick? Even if it gets in the way, a player cannot move it. But what if they did, especially if it is a moveable flag post? As the referee, do you tell them to put the flag back?
Moving a flag might look like a minor offence. You may not want to irritate a player by telling them to put the flag back. But what if they scored from the corner kick? How would you explain to the defending team? The defending team might very well complain that the restart was illegal.
So keep things simple. Take care of small things so you don’t have to worry about a possible big issue. Watch the video below. Tell the player to place the flag back before the kick.