In the clause "Someone did amazing," the word "amazing" is functioning as an adjective, describing the quality of the action or the person who performed it. This construction is correct and commonly used in informal language. Using "amazingly" as an adverb would slightly alter the meaning of the sentence. "Someone did amazing" emphasizes that the action or the person is extraordinary or impressive. On the other hand, if you say "Someone did amazingly," you are emphasizing the manner or method of how they did something in an impressive or extraordinary way. Both forms are grammatically correct, but the choice between them depends on whether you want to emphasize the action itself or the impressive manner in which it was done.

Yes, you're definitely correct that it would be better to use the adverb "amazingly." While it's not grammatically correct to use an adjective when an adverb is called for, in everyday speech you'll often hear constructions like the one in your example.

According to English as taught in classes, yes, you would need the adverb "amazingly." By all formal standards for English grammar, "You did amazing" is incorrect. However, in real life, when speaking casually, it is very common for people to use adjectives in places where an adverb is needed. Of course, "amazing" would be correct in situations where it is modifying a noun. "You were amazing," "You did an amazing job," etc.

The best , but not only, choice is to call "amazing" an adverb. Present participles can act as nouns, adjectives, or adverbs. (Just about the only thing they cannot do is act as active verbs.) So, after Sally runs in a race and performs well, you could say "Sally did amazing". That is a commonly spoken sentence in which amazing serves as an adverb and means the same as "Sally did amazingly well" You could also call it a noun, and that also would be a correct interpretation. The construction "Someone did NOUN" does make sense. For example, you can say "Someone did homework". That interpretation of your sentence would be less common but correct. It would be more commonly used in a negative: "Sally just doesn't do amazing." which means the same as "Sally just doesn't do the amazing". It is wrong to call it an adjective. What would it modify? That just doesn't make any sense because it has no linking verb to join it to the subject as would be the case in a sentence like "she became amazing". "Amazing" may look and feel like an adjective, and it is true that one can place any adjective into the sentence and obtain a correct sentence (such as "she just doesn't do happy"). However, the instant you do that, the adjective immediately transforms itself into a noun. The adjective interpretation just doesn't fly. You can "do" nouns but you cannot "do" adjectives. You can "become" ADJECTIVE. You can "be" ADJECTIVE. You can "grow" ADJECTIVE. You can "sound" ADJECTIVE. You can "look" ADJECTIVE. Those are linking verbs. But, you cannot "do" ADJECTIVE. The instant you say "Sally does ADJECTIVE", the adjective transforms itself into a noun. To know whether the speaker intends "amazing" as an adverb or as a noun it would be helpful to know the context or to hear the manner in which the words are spoken.

I would like to thank all of you for your explanation. Especially the long deep dive Jonathan made. Now I know it is both gramatically correct and commomly used. Regards