jumping , snapping on, instant kills

My 4th attempt to understand what is happening.

I see people jump out of windows rotate and snap onto my head. I die as soon as they point at me.

What is this EA;  Lag, aim-assist,cheats, de-sync.

It ruins the fun..and it happens often. Perhaps more with controller players, but i read they have hardly aimassist.

I would love some help