(Mishnah): If one was Mudar Hana'ah from his friend before Shemitah (the seventh year, in which whatever grows is Hefker), he may not enter his field, nor eat from Notos (trees whose foliage extend outside of his property);

In Shemitah, he may not enter the field, but he may eat from Notos.

If he vowed from [his friend's] food before Shemitah, he may enter his field, but he may not eat [even] from Notos;

In Shemitah, he may enter and eat.

(Gemara) Question: Why may he not enter [in Shemitah, in the Reisha]?

Answer: This is like R. Shimon ben Yakim said [above] - it is lest he delay. (The Torah authorizes him only for the time needed to take Peros.)

R. Yochanan explains our Mishnah to mean 'if one was Mudar Hana'ah from his friend before Shemitah, he may not enter his field, nor eat from Notos. In Shemitah, he may not enter the field, but he may eat from Notos. If he vowed in Shemitah, he may enter and eat. (The vow does not take effect, for the land does not belong to the Madir.)

Reish Lakish explains our Mishnah to mean 'if one was Mudar Hana'ah from his friend before Shemitah, he may not enter his field, nor eat the Peros. If he vowed in Shemitah, he may not enter his field, but he may eat the Peros. If he vowed from his food before Shemitah, he may enter his field, but he may not eat from the Peros. If he vowed in Shemitah, he may enter and eat.

Reish Lakish holds like R. Yosi;

[If the Mudar has nothing to eat,] R. Yosi says [that the Madir may not leave food in front of him and make it Hefker], because his vow preceded his Hefker. So Reish Lakish [forbids him to enter his field in Shemitah], because his vow preceded [the Torah's] Hefker (i.e. Shemitah).

Distinction: If his Hefker [preceded] his vow, no (he did not forbid himself to what is Hefker).

(R. Yonah citing R. Ba bar Chiyah citing R. Yochanan): R. Yosi [can hold like R. Yochanan; he] agrees about Hefker of the Torah (Shemitah), that it is permitted.