Is an illegal replacement entering the set considered an unnecessary delay?

An illegal replacement entering the set is indeed considered an unnecessary delay. This conclusion is based on the rules governing volleyball, which state that any actions which disrupt the flow of the game or are against the established regulations can result in a delay. When an illegal replacement occurs, it interrupts the normal operation of the match as officials need to address the situation, potentially leading to confusion and further stoppage. Thus, unsettling the pace of the game through these means qualifies as unnecessary delay, hence reinforcing the idea that maintaining proper conduct and adherence to the rules is crucial for the smooth progression of the match.