Jerusalem Talmud Shevuot 7:3

משנה: הַנֶּחְבָּל כֵּיצַד הָיָה מְעִידִין אוֹתוֹ שֶׁנִּכְנַס לְתוֹךְ יָדוֹ שָׁלֵם וְיָצָא חָבוּל וְאָמַר לוֹ חָבַלְתָּה בִי וְהוּא אוֹמֵר לֹא חָבַלְתִּי הֲרֵי זֶה נִשְׁבָּע וְנוֹטֵל. רִבִּי יְהוּדָה אוֹמֵר עַד שֶׁתְּהֵא שָׁם מִקְצָת הוֹדָייָה. כֵּיצַד אָמַר לוֹ חָבַלְתָּ בִי שְׁתַּיִם וְהַלָּה אוֹמֵר לֹא חָבַלְתִּי אֶלָּא אַחַת׃ MISHNAH: The injured one, how? They were testifying against him that one came to his hand whole and left injured⁵⁷And it is a reasonable inference that the second person was injured by the first.. He says, you injured me, but the other says, I did not injure; this one swears and collects. Rebbi Jehudah says, only if there was a partial admission. How is this? He said to him, you injured me twice but the other says, I injured you only once.

הלכה: הַנֶּחְבָּל כֵּיצַד כול׳. רִבִּי יְהוּדָה הָיָה קוֹרֵא חֲבָטִי. כָּל־זְמַן שֶׁהֵן חוֹכְכִין זֶה בָזֶה הֲרֵי זֶה נִשְׁבָּע וְנוֹטֵל. הָיָה נָשׁוּךְ בְּמָקוֹם שֶׁאֵינוֹ יָכוֹל לִישּׁוֹךְ עַצְמוֹ נוֹטֵל בְּלֹא שְׁבוּעָה. לְאַחַר זְמָן זֶה אוֹמֵר. חָבַלְתָּ בִּי. וְזֶה אוֹמֵר. לֹא חָבַלְתִּי. הֲרֵי זֶה כִשְׁאָר הַטַּעֲנוֹת. HALAKHAH: “The injured one, how,” etc. ⁵⁸Shevuot 6:2" href="/Tosefta_Shevuot.6.2">Tosephta 6:2, Bava qamma9:28 (S. Lieberman Tosefta kiFshutah Bava qamma p. 109.)“Rebbi Jehudah was calling them beaters⁵⁹In the parallel sources, חביבאי, חבבאי, כאי, הכאב which might support a reading חכאכי (or something similar) “wrestlers”.. Any time they are rubbing⁶⁰Or “wrestling”. one another, he swears and collects⁶¹If there are witnesses for a physical altercation but no witnesses for any detailed happening.. If he was bitten at a place where he could not bite himself, he collects without oath⁶²Shevuot.46b">Babli 46b, an Amoraic statement in the name of Samuel.. At a later time if one says, you injured me, but the other says, I did not injure, this is like any other claim⁶³This refers to the Mishnah. If the witnesses saw him whole and immediately after he was seen in an altercation he was seen injured, he swears and collects. But if the injury was only certified later, the general rules of evidence will apply to any claim..”