In Call of Duty Black Ops 3, you are able to run on walls for a short period of time. Though this is unrealistic, humans are actually able to run vertically up walls for a quite impressive distance. This is due to the force of friction. When you make contact with the wall with your hands and feet, you push them downwards in order to imbalance the forces. If the force of friction is greater than the force of gravity, you will be propelled upward when you run up the wall. This means that the force upwards is greater than the force of gravity downwards, causing a net force upwards accelerating you up the wall. However, you cannot run far up a wall from a stationary position. You must first get a running start in order to build up speed, energy and momentum which can then be used to get even higher.