Reference for Sanhedrin 66:1
ואין מחזירין לחובה מחזירין לזכות זכות גרידתא ואין מחזירין לחובה לזכות שהיא חובה
BUT NOT FOR CONDEMNATION, must mean, it can be reversed for acquittal, provided this involves only acquittal.<span class="x" onmousemove="('comment',' I.e., it does not cause damage to anyone else, e.g in the ease of the intentional desecration of the Sabbath, or of adultery. ');"><sup>1</sup></span> BUT NOT FOR CONDEMNATION. i.e., [there must be no reversal] in favour [of one] which is detrimental [to the other]. But to whose detriment can it possibly be? — That is no difficulty: It means to the detriment of the avenger of blood.<span class="x" onmousemove="('comment',' V. Num. XXXV, 19. It is a duty of the avenger of blood, the victim's nearest relative, to call the murderer to account (v. Mak. 12a; infra 45b; Mains. Yad, Rozeah I, 2), therefore in case the verdict were reversed for acquittal he would lose the opportunity of avenging his relative's blood. ');"><sup>2</sup></span>