Our Gemara tells the story of Rav Gidel who was negotiating on the purchase of a piece of land, but before he reached a final agreement Rabbi Aba came and bought it. Rav Gidel complained about Rabbi Aba’s behavior to Rabbi Zeira, who passed on the information to Rabbi Yitzhak Napha, who said that he would investigate the matter when Rabbi Aba came during the holidays.
Upon seeing him, Rabbi Yitzhak Napha asked Rabbi Aba what he thought of someone who sees a poor person finding a loaf of bread and takes it for himself before the poor man can take possession of it. Rabbi Aba responded that such a person would be declared a rasha. Rabbi Yitzhak Napha then demanded an explanation of why Rabbi Aba himself had behaved in that manner towards Rav Gidel in purchasing the land. Rabbi Aba replied that he was unaware that Rav Gidel was negotiating for the same parcel of land. When Rabbi Yitzhak Napha suggested that Rabbi Aba sell the land to Rav Gidel, Rabbi Aba refused to do so, saying that it was the first land he had ever purchased and he felt that it would be a bad omen to be forced to sell it. He was willing, however, to allow Rav Gidel to take it as a present. In the end, Rav Gidel declined to accept a gift – invoking the passage in Mishlei that discourages taking presents (see Mishlei 15:27) – and Rabbi Aba refused to tend the land, since he did not want to benefit from having purchased land that someone else wanted. With neither of them claiming the land as their own, it became known as “the field of the sages.”
The Me’iri explains that the field was not really considered ownerless, but it was left available to be used by the Sages as a place of recreation.