Is it permissible for there to be a person whose garment is trailing among the worshippers in the sutra behind the Imam?

The intent of the question is unclear. If it pertains to the ruling on isbal (letting one's garment hang below the ankles), an answer has already been provided. However, if the term "sutrah" (barrier) refers to the place behind the Imam, then only the most knowledgeable and pious among the people should stand there. This is so they can fulfill specific duties, such as alerting the Imam to an error or taking his place if needed. This precedence is not limited to prayer but extends to every gathering.