Which action is considered unnecessary delay in a match?

Unnecessary delay in a volleyball match refers to situations that disrupt the flow of play without valid reasons, thereby prolonging the match unnecessarily.

When evaluating the scenarios presented, it becomes evident that each situation contributes to delays in the game. An illegal substitute attempting to enter the set represents a delay because the violating action needs to be addressed by the officials, disrupting the game's progression. Similarly, a team requesting a time-out after it has run out is problematic because time-outs are designed to help teams maintain control over the match without altering the established rules; requesting one after the limit has been reached disrupts the flow for both teams. Lastly, a coach delaying a decision regarding an injured player introduces significant pause in the match, as officials must wait for a determination before resuming play.

Since all of these actions interrupts the game's flow and violate the principles of smooth play, they collectively lead to unnecessary delay. Therefore, recognizing that each action leads to such delays, the conclusion that all these scenarios result in unnecessary delay is valid.