He was using multi hack (kb, sphck, jpbg, jpsp etc...). I have demo if you do not believe me.
"laps" 264 STEAM_1:0:1477563669
https://www.mediafire.com/file/oniad76nnqpm786/[Fleshas_lt]_Knife-Arena_24_7.dem/file
This report goes for the knife Fleshas Server.
I had another clip of him killing me from behind with kb, but i missley got out of the server and my first demo wasn`t saved.
You can see in the other demo, on the end of it.

He just knifed you few times, jumped 260 and 270 and at the end he did sgs, you cant see from the demo if hes doing a strafe while jumping or he was over 100fps, thats not enough evidence 😀My advice next time follow him more closely what he is doing so that you can see through the demo.

First thing you need to write complains here: https://fleshas.lt/category/77/complains
Second fill the form like so:

1. The person you complaining about (nick) -
2. Server-
3. The reason-
4. The evidence (ss arba demo)-
5. Player steamid / ip (necessary!) -
   The third the demo is to short and there is no evidence, you didnt even spectate him.
   So complaint is rejected.