On the second hit, which contact by the setter is illegal?

In volleyball, the legality of a setter's contacts is governed by specific rules concerning the nature of the contact and the body parts that can be legally used. The correct answer highlights that using the kneepad to make contact with the ball, especially if there is prolonged contact, is illegal due to the rule that prohibits the ball from being played with any part of the body that is covered by clothing, including kneepads.

This is based on the principle that the ball must be clearly hit, and prolonged contact with a part of the body covered in such material can lead to unclear or ambiguous contacts, which are not permitted under official volleyball rules.

In contrast, using the foot, hip, or head to play the ball might not violate any specific regulation, assuming the contact is clean and does not involve prolonged play, as these body parts can be used effectively and legally in game play. The focus is on ensuring that the intention of the play is evident and that the ball is played in a clean manner, which is what the rules aim to maintain.