A player's ability to close out sets in tennis can be evaluated through several key statistics. These include their percentage of winning service games when at an advantage or serving for the set, break point conversion rates, and the percentage of points won on their opponent's serve during critical moments, such as set points. Additionally, the player's performance in tie-break situations, where mental toughness is crucial, can also serve as an indicator. Analyzing these metrics alongside their ability to maintain composure under pressure, particularly in high-stakes situations, provides a comprehensive view of their effectiveness in closing out sets.