Theoretically-

In the first clip, the other team has stated multiple times that their random teammate, Theoretically-, is cheating. It appears that the player has client side recoil macro and walls. You can see that the player is aiming through the wall and hipfire headshots. In the second clip, the player is obviously aiming through the walls and prefiring indestructible surfaces such as a concrete wall or a Castle barricade. The player attempts to flash an opponent with no information and aims at them through the wall. The same can be said for the third clip. In the fourth clip, you can see that the player has infinite ammo and continuously trying to shoot a player through the wall. In an instance, the player tries to prefire through a hard surface. In the fifth clip, you can say the same in regards to infinite ammo. The player does not reload their gun and basically has infinite bullets.