S.C. R. Civ. P. 13
Rules 13(a) through (i) are the same as the Federal Rules on counterclaims and cross-claims. These include and expand Code §§15-13-420, 15-15-30, 15-15-40, 15-15-50 and 15-15-70. Counterclaims arising out of the same transaction or occurrence that is the subject of the action are "compulsory" under Rule 13(a) and are barred by res judicata or estoppel by judgment if not asserted. All other counterclaims whether legal or equitable in nature are permissive, and may be pleaded against the opposing party. Separate trials on claims not directly related to the original action may be ordered by the court under Rule 13(i). Rule 13(j) is added to conform to State practice, in which there are courts of differing jurisdiction. This Rule 13 considerably broadens present State practice as to counterclaims, but will avoid much litigation and dispute whether the counterclaim or cross-claim is allowable under the old 1870 Code practice.