Common compounds: 撕开 (tear open), 撕破 (tear/rip apart), 撕碎 (tear to shreds). In internet slang, 撕 also means to argue/fight online: 互撕 (hùsī) = to quarrel publicly.
Left hand radical — the indexing component, marking 撕 as a hand-action verb. Tearing is a physical motion of grabbing and pulling apart. Same radical anchors a huge action family: 打 (hit), 拉 (pull), 推 (push), 扔 (throw), 拿 (take).
Right 斯 supplies the sound directly (sī = sī, no drift) and a faint flavor of cleaving/splitting — 斯 itself contains 斤 (axe), suggesting separation or cutting. A hand + axe-related phonetic = the action of ripping apart by hand.
