Q. Can you remove an acorn or twig that is under your feet when taking a stance?
It is loose and in a hazard? Then no. Rule 13-4c states that no loose impediment can be moved or removed from a hazard.
It is loose elsewhere? Then yes since it is a loose impediment.
But what if it's buried? Some would still say yes because a buried acorn or twig can still be considered a loose impediment. After all, it fell loose didn't it? Ha Ha Ha!
But seriously if it's buried, can you remove it either by picking/digging it out or shuffling your feet?
Simple rule to remember…
You have the right to take a stance but not build a stance.
The answer is NO. You are improving your lie if you dig out an object or shuffle your feet. The only place you can dig out the acorn or similar object or even shuffle your feet is on the tee box.
The official rule:
13-2. Improving Lie, Area of Intended Stance or Swing, or Line of Play
A player must not improve or allow to be improved:
• the position or lie of his ball,
• the area of his intended stance or swing,
• his line of play or a reasonable extension of that line beyond the hole, or
• the area in which he is to drop or place a ball,
by any of the following actions:
• pressing a club on the ground,
• moving, bending or breaking anything growing or fixed (including immovable obstructions and objects defining out of bounds),
• creating or eliminating irregularities of surface,
• removing or pressing down sand, loose soil, replaced divots or other cut turf placed in position, or
• removing dew, frost or water.
However, the player incurs no penalty if the action occurs:
• in grounding the club lightly when addressing the ball,
• in fairly taking his stance,
• in making a stroke or the backward movement of his club for a stroke and the stroke is made,
• in creating or eliminating irregularities of surface within the teeing ground (Rule 11-1) or in removing dew, frost or water from the teeing ground, or
• on the putting green in removing sand and loose soil or in repairing damage. (Rule 16-1).