As we have seen our Gemara is deliberating the conditions necessary for the High Court’s ruling to be accepted so that when it rules erroneously and that decision is acted upon by the majority of the Jewish community, the High Court will be obligated to bring a sin offering on behalf of the community, but the individuals will be free of the obligation to do so. The Mishnah on today’s daf (=page) teaches that if the muflah shel bet din – if the senior scholar among the judges – was missing when the decision was made, then the ruling will not be considered fully legitimate, and the court will not bring the sin offering on behalf of the community.
The muflah shel bet din heads the yeshivah, and the court scholars were all considered to be his students. Generally speaking, he was the person who was chosen to preside over the Sanhedrin. Rashi explains that we must be talking about a case where the muflah shel bet din was called away from the court for some reason, and another was appointed temporarily in his place, since all agree that were the court missing the full cohort of judges, their ruling would not be significant for the purposes of a communal sin offering.
Rashi, however, offers a different explanation, as well, suggesting that the muflah shel bet din may not have been a member of the Sanhedrin at all, perhaps because for technical reasons he could not have been appointed as a judge (e.g. he could not have children, which, as Rashi explains in Masechet Sanhedrin, causes us to fear that he does not have the requisite compassion and sensitivity needed for judgment as a member of the Sanhedrin). Nevertheless, due to his unique status as a scholar whose wisdom was needed by all, decisions should not have been made without consulting him. The Ri”d offers a similar explanation, pointing out that the Gemara occasionally talks of 72 scholars who legislate, indicating that there was an additional scholar who joined the Sanhedrin in decision making.