Caltrops is a skill located in the Assault (which can be found in the Alliance War skill tree). Caltrops is a base skill, and can be morphed into Anti-Cavalry Caltrops or Razor Caltrops.
Caltrops deals the following types of damage: Physical Damage. Which means that it gets buffed by the following blue champion point trees: Mighty, Piercing, Precise Strikes, Thaumaturge. Also the following red champion point trees protect against this skill: Hardy, Thick Skinned.