Knocked-out units and rebooting drones can be pinned to keep them inactive for longer. Any active unit can pin an inactive unit; this includes agents, guards and drones even when they are currently controlled by the agency. While a unit remains pinned, their KO timer or reboot timer does not tick down.
Inactive units are pinned whenever an active unit is on the same tile; this includes when an agent is dragging the other unit, and it includes when the active unit is a utility drone which can normally occupy the same tile as another active unit. When there are multiple inactive units on one tile, any active unit on the same tile will pin all of them at once.
A green triangular icon indicates that a unit is pinned. Usually, an agent or guard pinning another unit is shown crouched with their hand on the pinned unit, but this is purely graphical; the inactive unit is pinned regardless of the active unit's pose.
Agents cannot use melee weapons while they are pinning a unit, unless they attack the same guard they are pinning. An agent also cannot drop a unit they are dragging if they are also pinning a different unit on the same tile.
Guards can pin knocked-out agents, and do so when they have the opportunity to. When a guard is pinning an agent, he continue to pin until he is distracted by something else. If every agent remaining in a mission is pinned or lethally-wounded, the mission ends; if no other agent has exited the mission beforehand, then the mission is failed, otherwise the mission is “successful” but the pinned or lethally-wounded agent(s) are lost in the field. When this happens, the lost agent(s) can still be rescued from Detention Center missions.