Learn Hardcore French: Son frère est musicien et joue du violon sur une petite scène. - Her brother is a musician and plays the violin on a small stage.

In French, when you state someone’s profession, religion, or nationality in a simple way using être, you normally omit the indefinite article un / une:

Il est musicien. = He is a musician.
Elle est professeure. = She is a teacher.
Il est catholique. = He is Catholic.
Elle est française. = She is French.

So Son frère est musicien is the standard, neutral way to say His/Her brother is a musician.

You would add un only if you qualify or emphasize it with an adjective or phrase:

C’est un musicien célèbre. = He is a famous musician.
Son frère est un musicien de talent. = His/Her brother is a talented musician.

Notice that in those examples, French often prefers c’est + article (C’est un…) when you add a descriptive element.

Is Son frère est un musicien actually wrong?

It’s not grammatically wrong, but it sounds less natural in many contexts.

Son frère est musicien.
→ Normal, neutral statement of profession.
Son frère est un musicien incroyable.
→ Natural, you’re adding emphasis with an adjective.
Son frère est un musicien. (with no extra info)
→ Possible, but feels a bit marked/stylistic; you might use it to contrast:
- Son frère est un musicien, pas un ingénieur.
  His brother is a musician, not an engineer.

So: correct, but not the most idiomatic by itself.

Why is it joue du violon and not joue le violon or joue violon?

With musical instruments, French uses the structure:

jouer de + [instrument]

jouer du violon (= de + le violon)
jouer du piano
jouer de la guitare
jouer de la flûte
jouer de l’accordéon

The de + le contracts to du:

de + le violon → du violon

So:

Il joue du violon. = He plays the violin.

Jouer le violon is not the standard way to say play the violin in French.
You must use jouer du violon.

You also can’t simply say jouer violon in standard French.

What’s the difference between jouer du violon and jouer au tennis?

French distinguishes between instruments and games/sports:

For instruments:
jouer de + instrument
- jouer du violon
- jouer du piano
- jouer de la guitare
For sports/games:
jouer à + sport/jeu
- jouer au tennis
- jouer au football
- jouer aux cartes
- jouer à un jeu vidéo

So:

Il joue du violon. = He plays the violin.
Il joue au tennis. = He plays tennis.

Why is it du violon and not de le violon written separately?

In French, some preposition + article combinations contract into one word:

de + le = du
de + les = des
(but de + la and de + l’ do not contract)

Since violon is masculine singular (le violon):

jouer de le violon → jouer du violon

Writing de le violon is incorrect; you must use the contracted form du violon.

Why is it sur une petite scène and not dans une petite scène?

In French, when talking about performing on a stage, the usual preposition is sur:

Il joue sur scène. = He performs on (the) stage.
Elle danse sur une grande scène. = She dances on a big stage.

Sur indicates you are on top of a surface, which fits the idea of a stage as a platform.

Dans une scène would mean “inside a scene” in the sense of a scene in a movie/play, which is a different meaning (like a part of a story, not a physical stage).

Could I move sur une petite scène earlier in the sentence?

Yes, but the original order is the most natural:

Son frère est musicien et joue du violon sur une petite scène.
→ Very natural.

Possible but less neutral:

Son frère est musicien et, sur une petite scène, joue du violon.

Putting sur une petite scène at the end is the default: French usually places complements of place and manner after the verb phrase, similar to English (plays the violin on a small stage).

Why is it une petite scène and not une scène petite?

Most adjectives normally come after the noun in French, but a group of very common, short adjectives often come before the noun. Petit / petite is one of those.

So both:

une petite scène
une scène petite

are technically possible, but:

une petite scène is normal and idiomatic.
une scène petite sounds unusual and might be used only for strong emphasis or literary effect, like focusing on size in a special way.

In practice, you should say une petite scène.

Why does petite end with -e here?

Adjectives in French must agree in gender and number with the noun they describe.

scène is feminine singular (la scène).
The base adjective is petit (masc. sing.).
Feminine singular form: petite (add -e).

So:

un petit garçon = a small boy
une petite fille = a small girl
une petite scène = a small stage

If the noun were masculine, it would be:

un petit théâtre (a small theatre).

Is scène feminine or masculine? How do I know?

In this sentence, the article une tells you scène is feminine:

une scène, la scène → feminine
un scène (masculine) would be incorrect.

Unfortunately, the gender of nouns in French is mostly arbitrary and must be memorized with the noun:

la scène (f.) = the stage / the scene
la table (f.), le livre (m.), la voiture (f.), le problème (m.), etc.

A good habit is always to learn new nouns with their article:
la scène, not just scène.

Is musicien masculine or feminine here? What would the feminine form be?

In Son frère est musicien, the context (frère = brother) shows the person is male.

musicien is the masculine form.
The feminine form is musicienne.

Examples:

Son frère est musicien. = His/Her brother is a musician.
Sa sœur est musicienne. = His/Her sister is a musician.

Does French present tense here mean “is a musician and plays” or “is being a musician and is playing”?

The French present tense covers both English simple present and present continuous.

So:

Son frère est musicien et joue du violon sur une petite scène.

can mean:

His/Her brother is a musician and plays the violin on a small stage (in general).
or His/Her brother is a musician and is playing the violin on a small stage (right now).

Context decides which reading is intended, but grammatically, one French form covers both English forms.

Is there anything special about the pronunciation, like liaisons, in this sentence?

Important points of pronunciation:

Son frère
- Final n in son is nasalized; frère starts with fr-. No liaison: /sɔ̃ frɛʀ/.
est musicien
- Often there is a liaison between est and musicien:
  - est‿musicien → /ɛ tmy.zi.sjɛ̃/
  - You pronounce the t sound linking into musicien.
joue du violon
- joue ends in a silent -e: /ʒu/.
- du: /dy/.
- violon: /vjɔ.lɔ̃/ (final -n is nasal; the vi- is like “vyo”).
une petite scène
- une: /yn/ (nasal n).
- In petite, the final -e is silent, but the t is pronounced: /pə.tit/.
- scène: /sɛn/ (like “sen”).

There’s no liaison between joue and du, or between violon and sur in standard speech.