Final answer:
The correct term for a golfer scoring the best round in a four-round tournament is 'Tournament Leader', as it signifies leading the entire tournament's cumulative score.
Step-by-step explanation:
A golfer scoring the best round in a four-round tournament is referred to as the Tournament Leader. This term is used because the individual has the best score after a particular round, indicating their position on the leaderboard above all other competitors. In golf, the term Winning Round is not necessarily indicative of leading a tournament, as it could refer to just a single round rather than the cumulative score across multiple rounds. Similarly, Top Swing is not a term generally used for scoring or standings in golf. Finally, Best Score can refer to the best score of a single round or hole, but it does not always convey the idea of leading a tournament.