As far as esports go, CS:GO is among the ones with the highest technical requirements and skill caps. Certain aspects of a lot of games challenge it, but the number of factors that go into CS:GO, both mechanically and strategically, give it a strong argument.
Especially where guns factor in, the game is incredibly difficult to even learn, let alone execute. Even just getting a grasp of spray patterns for multiple guns is inherently difficult. Add in how moving and jumping/ falling affects it, and you've got a lot to remember.
Remembering all of that, this shot by Nicholas "nitr0" Cannella is all the more impressive. On top of a train and across the A bomb site, he lands a jumping headshot that ended his opponent before they could do much.
The caster's reaction sums up the situation far better than Twitch chat screaming "VAC" left and right. Just a stunned "what?" is about all that can be said about the shot.