Learn Hardcore Polish: Moje rodzeństwo gra w siatkówkę na boisku. - My siblings play volleyball on the field.

moje = “my” for neuter singular (and also non‑masculine personal plural)
rodzeństwo = “siblings / brothers and sisters” (a collective noun, neuter singular)

So you get:

moje rodzeństwo – my siblings
not:
moja rodzeństwo (would match feminine)
moi rodzeństwo (would match masculine‑personal plural)

You treat rodzeństwo grammatically like words such as dziecko (child), krzesło (chair): moje dziecko, moje krzesło, moje rodzeństwo.

Why is it gra (singular) and not grają (plural), when “siblings” are clearly more than one person?

In Polish, rodzeństwo is a collective noun and behaves like a singular noun in grammar, even though it refers to several people.

So:

Moje rodzeństwo gra w siatkówkę.
literally: My siblings plays volleyball. (ungrammatical in English, but normal in Polish)

If you want a grammatically plural subject with grają, you must use an actually plural noun, e.g.:

Moje siostry grają w siatkówkę. – My sisters play volleyball.
Moi bracia grają w siatkówkę. – My brothers play volleyball.
Mój brat i moja siostra grają w siatkówkę. – My brother and my sister play volleyball.

Can I use rodzeństwo to say how many siblings I have, like “I have two siblings”?

Not in a simple 1:1 way. Rodzeństwo is usually treated as a mass/collective noun, so you don’t naturally say:

Mam dwa rodzeństwa. ❌ (sounds wrong in everyday speech)

Instead you usually say:

Mam dwoje rodzeństwa. – I have two siblings.
(using a collective numeral: dwoje, troje, czworo, etc.)

But even more common and clearer in real life is to specify:

Mam brata i siostrę. – I have a brother and a sister.
Mam dwóch braci. – I have two brothers.
Mam trzy siostry. – I have three sisters.

So rodzeństwo is good for talking about your siblings as a group, not for listing numbers in a simple way.

Why do we say gra w siatkówkę, with w, instead of just gra siatkówkę?

With games and sports, Polish normally uses:

grać w + [sport/game in the accusative]

Examples:

grać w siatkówkę – to play volleyball
grać w piłkę nożną – to play football/soccer
grać w koszykówkę – to play basketball
grać w szachy – to play chess

So w is part of the standard pattern with games and sports.
By contrast, with musical instruments you use na, not w:

grać na gitarze – to play the guitar
grać na pianinie – to play the piano

Grać siatkówkę without w sounds foreign or incorrect.

Why is it siatkówkę and not siatkówka in this sentence?

Because w siatkówkę requires the accusative case.

The base (dictionary) form is siatkówka (nominative).
Feminine singular accusative typically ends in ‑ę:
- siatkówka → siatkówkę
- kawa → kawę
- kolacja → kolację

So the structure is:

grać w + [accusative]
→ grać w siatkówkę

Could I say gra w siatce or gra w siatkę instead of gra w siatkówkę?

Colloquially, yes, but with a nuance:

gra w siatkówkę – standard, neutral, correct in all contexts
gra w siatkę – very common informal spoken Polish (shortened form)
gra w siatce – generally wrong in this meaning; w siatce would mean “in a net / in a bag”

So in normal speech you’ll often hear:

Gramy w siatkę. – We’re playing volleyball. (informal)

For learners, it’s safest to use the full form w siatkówkę, especially in writing or formal contexts.

Why is it na boisku and not na boisko?

Because the sentence describes location (“on the court”), not movement towards the court.

Polish preposition na can take:

Locative – where something is (static location):
- na boisku – on the court / on the pitch
- na stole – on the table
- na uczelni – at the university
Accusative – direction, movement onto:
- na boisko – onto the court / to the court
- na stół – onto the table
- na uczelnię – to the university (to attend/go there)

Your sentence is about where the action happens, so it uses na + locative → na boisku.

Why does boisko become boisku here?

Because boisko is a neuter noun, and na (with the meaning “on/at”) governs the locative case, which for neuter nouns often ends in ‑e or ‑u.

nominative: boisko – a court / pitch / playing field
locative: (na) boisku – on the court

Some other examples:

miasto → w mieście – in the city
łóżko → w łóżku – in bed
jezioro → w jeziorze – in the lake

The exact locative ending is something you generally have to learn with each noun, but boisko → boisku is the standard form.

Can I change the word order, like Na boisku moje rodzeństwo gra w siatkówkę?

Yes. Polish word order is quite flexible, and all of these are grammatically correct:

Moje rodzeństwo gra w siatkówkę na boisku.
Na boisku moje rodzeństwo gra w siatkówkę.
Moje rodzeństwo na boisku gra w siatkówkę.

The differences are mostly about emphasis and information structure:

Starting with Na boisku emphasizes the location: On the court, my siblings play volleyball (as opposed to somewhere else).
Starting with Moje rodzeństwo emphasizes who is doing the action.

As a learner, your original word order is perfectly natural and a good default.

Does this sentence mean “My siblings play volleyball (as a habit)” or “My siblings are playing volleyball (right now)”?

It can mean either, depending on context. Polish doesn’t have a separate continuous tense like English “are playing”. The simple present covers both:

Moje rodzeństwo gra w siatkówkę na boisku.
- could be: My siblings play volleyball on the court. (general habit)
- or: My siblings are playing volleyball on the court. (right now)

If you want to make “right now” really clear, you can add an adverb:

Moje rodzeństwo teraz gra w siatkówkę na boisku. – My siblings are playing volleyball on the court now.