The omoplata attacks the shoulder by trapping one of the opponent's arms between your legs and rotating their torso until the shoulder joint gives. From closed guard you swing your hips out, swing your leg across their back, sit up, and rotate their arm down and outward. It targets the same shoulder structures as the kimura, but uses your legs rather than your arms as the primary lever.
The omoplata is also a powerful sweep option: if the opponent rolls forward to escape, you follow and can end up on top. This makes it simultaneously a submission and a reversal, creating a double threat from the same entry.
It links tightly with the triangle — both attack from a similar hip position — and the armbar, forming a three-way attack system from guard.
For the full technique and variations, see Omoplata.