What is the priority of a referee when refereeing the defence in an on-ball matchup?

In an on-ball matchup, the priority of a referee is to focus on the illegality of the defensive player. This is crucial because the defensive player often has a responsibility to maintain legal guarding position and avoid committing fouls, such as reaching in, pushing, or holding the offensive player. Recognizing these illegal actions by the defender is essential for maintaining the integrity of the game and ensuring fair play.

While observing the position of the ball and the legality of the offensive player are important, the referee's primary responsibility in this specific context is to monitor the defensive player's actions. This vigilance helps to uphold the rules of the game and promotes safety, preventing the defensive player from gaining an unfair advantage. Recognizing fouls committed by both players is also relevant, but in the context of an on-ball matchup, the specific focus on the defensive player's legality takes precedence.