Well, my most reports go for ESP-hackers, that have an insane mystical knowledge of my position.
Even if I didnt't attack them and planned to let them pass, they run directly towards the stone I am hiding at.
It's so 100% obvious they can see through the stone or have a point on their map...
And nope I am not moving, not shooting or throwing a nade, nope nothing...
I am moving crouched to sneak and I am not even reloading or using anything.
Each evening I report 6-12 players like that.
I keep watching them until the next fire fight to see how they move and aim.
Best was that guy who pinged a movable conainer-box 5 km away, those blue things with the catapillars...
I wondered why he pinged it, but when he arrived he directly went in and shot at a player that was hiding in a corner of that container!
Hillarious obvious he was able to see the position of that player from 5 km and through the walls...
ESP-hack is soo obvious if you watch those idiots playing but pretty much undetectable for anticheat.