Spiky trap.
The item id for Caltrop in unturned is 382. You can use this ID with the commands below to spawn the item, give it to a player or buy it on a modded economy server.
Useable: Barricade
Build: Spike
Size_X: 1
Size_Y: 1
Size_Z: 0.25
Health: 15
Range: 4
Radius: 0.1
Offset: 0.125
Player_Damage: 20
Zombie_Damage: 40
Explosion: 36
Blueprints: 1
Blueprint_0_Type: Barricade
Blueprint_0_Supply_0_ID: 71
Blueprint_0_Supply_0_Amount: 2
Blueprint_0_Build: 27
Has_Clip_Prefab: false