[quote="Yus3i":3skby5cz]During a local this situation re-occured, and I think the judge didn't rule it correctly. I was playing Goat format, I had on my field a "skill drain" set; my opp summons "chaos sorcerer" in atk position, and declares prio to ban my monster on the field. I immediately chain "skill drain", so the effect is negated. The opponent proceeds to declare attack on my monster with "chaos sorcerer". I explain that "skill drain" negates effects, but still allows the activation; so "chaos sorcerer" can't attack. My opponent asks judge, judge says it can. I search online the ruling, but I can't find anything in either the "chaos sorcerer" and "skill drain" ruling. Still, in the "black luster soldier - envoy of the beninning" ruling, this exact scenario is ruled and the chaos monster can't attack. Can i safely assume it is the same for "chaos sorcerer"? Is there any better proof I could use to prove that? Thanks.[/quote:3skby5cz]
https://db.ygoresources.com/card#5833This is the card database with rulings in the FAQ section, it does also mention what happens if Chaos Sorcerer's effect is negated (which is the relevant point here) vs its activation being negated. The FAQ is in japanese, so you'll have to use a browser extension or something similar for the translation, but it is the kind of proof you're looking for, because you are correct: In the scenario you described, the Chaos Sorcerer cannot declare an attack.
In the end the (head-)judge's word is the law for the event taking place, even if they are clearly wrong, so if they stick to their ruling even after you provided proof, there is sadly nothing you can do at that time.
Hope this helps
Yus3i
Jon-Stark
Ir0n