Which situation results in a player not incurring a penalty stroke?

Removing loose impediments in play does not result in a player incurring a penalty stroke because the Rules of Golf allow a player to clear loose impediments without restriction. Loose impediments include natural objects such as leaves, twigs, or stones that are not fixed or growing, and their removal is part of maintaining a fair and playable course. This action is beneficial and promotes good course management, as it can help ensure a clear path for the player's shot without affecting their lie or stance.

In contrast, the other scenarios outlined can lead to penalties. Failing to mark a ball before lifting it is a breach of the rules, as it can lead to misunderstandings about the position of the ball. Accidentally hitting the ball during a swing is typically penalized unless very specific conditions apply, as it can affect the outcome of play. Improving one's stance before executing a stroke is also against the rules, as it can provide an unfair advantage by altering the playing conditions. Therefore, the act of removing loose impediments stands out as a permissible and non-penalized action in the game of golf.