There is a bug in Call of Duty: Modern Warfare which allows you to drop below ground level in some maps and hit undisturbed from that irregular position, as streamer Aimbotcalvin has experienced.
Apparently, the bug that allows you to hide under the map and hit undisturbed from this position reappears in Call of Duty: Modern Warfare and to pay for it, in this case, was the streamer Calvin ‘Aimbotcalvin’ Chau who vented in a way quite colorful during a video streaming.
Aimbotcalvin, from SoloMid Team, was just about to get a Tactical Nuke when someone hit him, without understanding at first what exactly had happened. The next killcam revealed the arcane: the player was below ground level on the Call of Duty: Modern Warfare Port of Verdansk map.
It is a bug present in Call of Duty: Modern Warfare that allows you to find yourself below the map, in an area that obviously should not be accessible but from which you are invisible to players who are on the surface, thus being able to hit undisturbed.
Having collected 26 consecutive kills, Aimbotcalvin found himself four kills from the Tactical Nuke when he was hit in an irregular manner, so it is also understandable the reaction of the streamer on the video to what happened, as visible below.