It is not permissible to throw pebbles on behalf of others without being authorized except in the case when a person, such as a young child or an unconscious person, cannot authorize another person to do so.
Sheikh Faysal Mawlawi, Deputy Chairman of the European Council for Fatwa and Research, states: “If a person cannot throw the pebbles himself during Hajj for some legal excuse, such as sickness, pregnancy, old age, or weakness, it is permissible for that person to authorize someone to throw the pebbles on his behalf if he cannot bear the overcrowded conditions of the pilgrims and is at risk of being harmed. The Shafi`i scholars made the condition that the excuse should be one that it is not likely to be removed before the Days of Tashriq.
The one who is authorized must throw his pebbles first, after which he can throw the pebbles on behalf of the other person. It is not permissible to throw pebbles on behalf of others without being authorized. The only exception is if the person cannot authorize another person to do the throwing on his behalf. For example, the father or guardian of a young child can throw the pebbles on his behalf without being authorized. According to Hanafi scholars, the associates of the unconscious person are permitted to throw the pebbles on his behalf without being authorized.”