The gemara tries to prove that one can take the law into their own hands by physically forcing their slave to leave their home after the time of his slavery has expired, even though there isn't any loss. R' Nachman Bar Yitzchok argues that even the opinion who says that normally one cannot take the law into his own hands would agree here because it is speaking about a case where he was married to a shifcha, who is now forbidden to him, so he has a right to stop him from doing an issur. Both Rabbeinu Chananel and the Rambam (Hil. Avadim 3:5) rule that the master would be patur for injuring the eved when he is throwing him out of the house, as the braisa seems to imply, that he is patur. But, it is very possible that it is assur l'chatchila to hit him and to cause him physical harm, even when trying to stop him from an issur.
However, Rashi writes explicitly:
ורשאי להלקותו ולהפרישו, דהאי דינא לאו לנפשיה הוא
Rashi implies that one is allowed to physically stop someone from doing an issur, even if it will casue him harm. This is a tremendous chiddush. Although we know that beis din can force people to do mitzvos by hitting them, and presumably also stop them from doing issurim by beating them, where do we find that within the personal obligation of tochacha we would allow one to violate the issur of chovel b'chaveiro and hit his friend?