This happened to a player who found an invisible wall on Nuke yesterday. This wall blocks all incoming bullets on one side but allows anyone on the other side to shoot back.
In the video provided, the player climbed up the ladder that leads to the T roof where an enemy player can be seen standing next to some pipes. The two players then saw each other and the CT ducked back to take cover. When he popped back up, the player shot him seemingly in the head multiple times.
If this was a normal circumstance, the round would have been over. Unfortunately for the player, his bullets hit what looked like an invisible wall that protected his opponent. He fired off an entire magazine into the wall before the player retaliated—the CT’s bullets weren’t affected by the invisible wall.
To explain what happened, someone on the CS:GO subreddit chimed in and said that when using “vcollide_wireframe 1” in the console, you can see each in-game item’s collision boxes. The pipe that the CT player was standing behind was larger than it appeared and certain guns can’t penetrate these collision boxes.
It’s frustrating as a player to outplay and out-aim an enemy just to get killed by an element that wasn’t in your control. The developers will likely need to patch out the extended collision box soon.