Learn Hardcore Portuguese (Portugal): Não risques o tapete com os teus sapatos.

Portuguese is a “pro-drop” language, which means subject pronouns are often omitted. The verb ending -os in riscos already tells you the subject is tu (you), so you don’t need to say tu explicitly.

Why does the sentence use Não riscos instead of an imperative like risca or risques?

Strictly speaking, riscos is the present indicative form (you scratch), so Não riscos reads like “you don’t scratch…”.

To give a direct prohibition to tu in European Portuguese, you’d use the present subjunctive: Não risques o tapete com os teus sapatos.
In casual Brazilian Portuguese you sometimes hear não + indicative (e.g. não vai), but that is non-standard in Portugal for tu.

Why is the definite article o used before tapete?

In Portuguese you generally need the definite article before singular, countable nouns when they are specific or known:

o tapete = “the rug/carpet”.
Omitting the article (just tapete) would sound incomplete or generic in most contexts.

Could we drop the article and just say Não risques tapete com os teus sapatos?

No. In standard European Portuguese you almost always keep the article before singular, concrete objects. Without o, it sounds ungrammatical.

What’s the difference between teus sapatos and seus sapatos?

teus sapatos matches the informal second-person pronoun tu.
seus sapatos would match você, ele/ela or a third person.
Since this sentence addresses someone as tu, you pair it with teu/teus.

Why do we say os teus sapatos instead of just teus sapatos?

In European Portuguese it’s very common to keep the article before possessives, especially in spoken and regional varieties. In Brazil you’d more often hear teus sapatos without os, but in Portugal os teus sapatos is idiomatic.

Why is the preposition com necessary here?

com expresses the instrument or means: “with your shoes.”
Portuguese verbs like riscar require com when you say what you’re using to scratch or mark something.

Is tapete different from carpete?

Yes.

tapete usually means a rug or mat, often moveable.
carpete refers to wall-to-wall carpeting that covers the floor.

What other verbs could express damaging a rug with shoes?

You might also hear:

arranhar (to scratch/snag)
esfregar (to rub)
danificar (to damage)
But riscar is most common for leaving visible scratches or marks.

How would you reformulate the sentence for a formal “you” (você) or for a group (vocês)?

Formal singular (você): Não risque o tapete com os seus sapatos.
Plural (vocês with informal or formal you): Não risquem o tapete com os vossos sapatos.