In the course of discussing whether the evening service is obligatory or optional, the Gemara relates the following story:
The Sages taught: There was an incident involving a student, who came before Rabbi Yehoshua. The student said to him: Is the evening prayer optional or obligatory? Rabbi Yehoshua said to him: Optional.
The same student came before Rabban Gamliel and said to him: Is the evening prayer optional or obligatory? Rabban Gamliel said to him: Obligatory.
The student said to Rabban Gamliel: But didn’t Rabbi Yehoshua tell me that the evening prayer is optional? Rabban Gamliel said to the student: Wait until the ba’alei terisin – “the masters of the shields,” a reference to the Torah scholars who battle in the war of Torah, enter the study hall, at which point we will discuss this issue.
When the ba’alei terisin entered, the questioner stood before everyone present and asked: Is the evening prayer optional or obligatory?
Rabban Gamliel said to him: Obligatory. In order to ascertain whether or not Rabbi Yehoshua still maintained his opinion, Rabban Gamliel said to the Sages: Is there any person who disputes this matter?
Rabbi Yehoshua said to him: No, no one disagrees. In deference to the Nasi, he did not wish to argue with him publicly (Tziyyun Le-Nefesh Ḥayya). Rabban Gamliel said to Rabbi Yehoshua: But was it not in your name that they told me that the evening prayer is optional?
Rabban Gamliel said to Rabbi Yehoshua: Yehoshua, stand on your feet and they will testify against you. Rabbi Yehoshua stood on his feet and said: If I were alive and the student were dead, the living can contradict the dead, and I could deny issuing that ruling. Now that I am alive and he is alive, how can the living contradict the living? I have no choice but to admit that I said it.
In the meantime, Rabban Gamliel, as the Nasi, was sitting and lecturing, and Rabbi Yehoshua all the while was standing on his feet, because Rabban Gamliel did not instruct him to sit. He remained standing in deference to the Nasi. This continued for some time, until it aroused great resentment against Rabban Gamliel, and all of the people assembled began murmuring and said to Ḥutzpit the disseminator: Stop conveying Rabban Gamliel’s lecture. And he stopped.
While Rashi interprets ba’alei terisin as the scholars who debate one another in the “battle of Torah,” the Arukh offers the more literal definition of “shield bearers,” that is, soldiers or police officers who were appointed by the government to support the Jewish leadership. In this story, as well as similar ones that appear in other places in the Talmud, we see that Rabban Gamliel desired to establish Yavneh as the central address for singular leadership and law in the post-Temple era. In his disagreements with Rabbi Yehoshua – one of Rabban Yohanan ben Zakkai’s closest students – he aims to clarify and establish his halakhic decisions as binding.