English Explanation of Mishnah Sanhedrin 6:1

When the trial is completed he [the condemned] is led forth to be stoned.
The place of stoning was outside of the court, as it is says, “Bring out him that has cursed” (Lev. 24:14).
A man was stationed at the door of the court with the handkerchiefs in his hand, and a man on a horse was stationed at a distance yet within sight of him. If one says, ‘I have something [further] to state in his favor’, he [the signaler] waves the handkerchief, and the man on the horse runs and stops them. And even if he [the convict] himself says, ‘I have something to plead in my own favor’, he is brought back, even four or five times, providing, however, that there is substance in his assertion.
If then they find him innocent, they discharge him.
But if not, he goes forth to be stoned, and a herald precedes him [crying]: so and so, the son of so and so, is going forth to be stoned because he committed such and such an offense, and so and so are his witnesses. Whoever knows anything in his favor, let him come and state it.”
The sixth chapter of Sanhedrin deals with the execution by stoning of a person convicted of a capital crime. Although stoning sounds like quite a brutal death, and it certainly must have been painful, as we read the chapter try to keep in mind that execution was an acceptable punishment in all societies in the ancient world. It is also mentioned numerous times in the Bible. Stoning as a mode of execution is also mentioned many times in the Bible. It would be anachronistic of us to expect the Rabbis to exclude the possibility of execution. On the other hand, you should note how cautious the Rabbis were in even theoretically punishing someone through execution. The possibility of the convict’s being exonerated always remained open, even until the last moment. Even while performing the execution the Rabbis were extremely concerned for the respect shown to the convict’s body, as we will see in later mishnayoth. Finally, we must keep in mind that the requirements for proper testimony were so strict that convicting someone would be extremely difficult. Indeed, execution was probably rarely, if ever, carried out, at least according to the rules of Jewish law.
Our mishnah describes the process of stoning, one of the four methods of execution which the mishnah describes. The other three will be described later.
The stoning was not done at the place of the trial, but rather further away from the city. This is proven from a verse in Leviticus which describes taking out the person who cursed God, a capital crime according to the Torah. According to our mishnah “taking out” implies that they took him out of the city.
There are two functionaries described in our mishnah: one who would hold a handkerchief, or flag of some sort and would stay near the court, and one who would ride on a horse and stand some distance from the first man, but still be able to see him. If someone came and offered testimony that would exonerate the convict, the man with the handkerchief would wave and the man on the horse would see the sign and ride out and halt the execution. Even if the convict himself brought up new testimony they would halt the execution, provided he made a substantial claim. If at any time they found in his favor, he would be immediately dismissed. Although this might be a rare occurrence, being so late in the process, nevertheless the mishnah considers it important to remind us that it is never to late to change a verdict from guilty to innocent.
As they are bringing the convict out to be stoned a herald would walk in front of him announcing who he was and why he was being executed. We might have assumed that the purpose of such a custom would be to make an example of the accused, and thereby prevent others from repeating his crime. However, the mishnah does not describe this as the reason for the herald’s crying out. Rather, this is yet another opportunity to find someone to exonerate the convict, and thereby prevent an innocent person’s blood from being shed.