Falling Net

From Dungeon Master's Guide, page 122.

Mechanical trap

This trap uses a trip wire to release a net suspended from the ceiling.

The trip wire is 3 inches off the ground and stretches between two columns or trees. The net is hidden by cobwebs or foliage. The DC to spot the trip wire and net is 10. A successful DC 15 Dexterity check using thieves' tools breaks the trip wire harmlessly. A character without thieves' tools can attempt this check with disadvantage using any edged weapon or edged tool. On a failed check, the trap triggers.

When the trap is triggered, the net is released, covering a 10-foot-square area. Those in the area are trapped under the net and restrained, and those that fail a DC 10 Strength saving throw are also knocked prone.

A creature can use its action to make a DC 10 Strength check, freeing itself or another creature within its reach on a success. The net has AC 10 and 20 hit points.

Dealing 5 slashing damage to the net (AC 10) destroys a 5-foot-square section of it, freeing any creature trapped in that section.