Learn Hardcore Japanese: watasi ha syuumatu ni tomodati to issyo ni kouen de supootu wo simasu. - I play sports in the park with a friend on the weekend.

In this sentence, 私 is also the subject in meaning, but Japanese separates “topic” (は) from “grammatical subject” (often marked by が). For simple “I do X” sentences, learners usually just learn X は Y です / Y をします as “I …”.

You could omit 私 entirely if it is clear from context who “I” is:

（私は）週末に友達と一緒に公園でスポーツをします。
= “(I) play sports at the park with my friends on the weekend.”

What’s the difference between 週末に and 公園で? Why に for one and で for the other?

They are marking different kinds of information:

週末に – に marks a point in time:
- 週末に = “on the weekend”
- Other examples: 3時に (at 3 o’clock), 月曜日に (on Monday)
公園で – で marks the place where an action happens:
- 公園で = “at/in the park”
- Other examples: 家で食べます (eat at home), 学校で勉強します (study at school)

So the pattern is:

[time + に] + [place + で] + [action]

週末に (when) + 公園で (where) + スポーツをします (do sports).

Why does 一緒 also have に after it (一緒に)? Is that the same に as in 週末に?

The particle に after 一緒 is doing something different.

一緒に is a fixed expression meaning “together”.
Grammatically, に turns 一緒 (“togetherness”) into an adverb: “in a together way” → “together”.

So:

一緒に行きます = “(We) go together.”
一緒に食べます = “(We) eat together.”

This に is not marking time or destination like in 週末に.
You can think of 一緒に as one unit: “together”.

Do I really need both 友達と and 一緒に? Aren’t they saying the same thing?

They overlap in meaning, but they’re not strictly redundant. All of these are possible:

友達とスポーツをします。
- Literally: “I do sports with friends.”
- Meaning: you do sports with your friends.
友達と一緒にスポーツをします。
- Literally: “I do sports together with friends.”
- Emphasises the idea of doing it together as a group.
一緒にスポーツをします。
- Literally: “I do sports together.”
- It implies “with someone”, but doesn’t say who.

In your sentence, 友達と一緒に makes it crystal clear that:

you’re doing it with friends (友達と)
and you’re doing it together as a shared activity (一緒に)

It’s very natural Japanese to use X と一緒に.

What exactly does the particle と after 友達 mean?

Here, と means “with” (companionship).

友達と = “with (a) friend / friends”
Patterns:
- 誰と行きますか。 – “Who are you going with?”
- 家族と住んでいます。 – “I live with my family.”

This と has other uses (like “and” when listing nouns: りんごとバナナ = “apples and bananas”), but in this sentence it’s the “with” meaning.

Why is スポーツ followed by をします? What does を do here?

を marks the direct object of the verb – the thing that the action is done to.

スポーツをします = literally “do sports”
- スポーツ = sports
- を = object marker
- します = do (polite form of する)

So:

何をしますか。 – “What will you do?”
スポーツをします。 – “I will do sports / I play sports.”

In casual speech, people sometimes drop を when it’s obvious, but as a learner, it’s good to keep it:

スポーツする (casual)
スポーツをする (also fine; more explicit)

Why is the verb します at the end? Can I say しますスポーツ like in English?

Japanese basic word order is:

Subject – Object – Verb (SOV)

English is:

Subject – Verb – Object (SVO)

So in Japanese:

私は（S）スポーツを（O）します（V）。

The verb almost always comes at the end of the clause.
Putting します before スポーツ (しますスポーツ) is ungrammatical.

More examples:

本を読みます。 – I read a book.
音楽を聞きます。 – I listen to music.
映画を見ます。 – I watch a movie.

What’s the difference between します and する?

Both mean “to do”, but they differ in politeness level:

する – plain / dictionary form (casual)
します – polite -ます form

Use します:

with people you’re not close to
in class, with teachers, in most writing, etc.

Use する:

with close friends, family, informal messages, etc.

Your sentence is in the polite style:

スポーツをする。 – casual
スポーツをします。 – polite (what you have)

Can I say 公園にスポーツをします instead of 公園でスポーツをします?

No, 公園にスポーツをします is not natural.

に after a place often marks a destination or location of existence:
- 公園に行きます。 – I go to the park. (destination)
- 犬が公園にいます。 – There is a dog in the park. (exists there)
で after a place marks where an action takes place:
- 公園でスポーツをします。 – I play sports at the park.

So:

公園に行きます。 (go to the park)
公園でスポーツをします。 (do sports in/at the park)

Why does 週末 take に, but in English we just say “on weekends” or “at the weekend”?

In Japanese, に is the normal particle for many specific times:

週末に – on/at the weekend
土曜日に – on Saturday
7時に – at 7 o’clock
夏に – in summer

You can loosely think of Japanese に as covering English “on / at / in” when they are used for time. Which English preposition you choose depends on English rules, not Japanese ones.

So:

週末にスポーツをします。
= I play sports on the weekend.
(or “at the weekend” in British English)

Can I say 週末は友達と一緒に公園でスポーツをします instead? What’s the difference between 週末に and 週末は?

Yes, you can say that. The nuance changes a bit:

週末に友達と一緒に公園でスポーツをします。
→ Neutral statement: on the weekend, I (sometimes/usually) play sports with my friends at the park.
週末は友達と一緒に公園でスポーツをします。
→ 週末 becomes the topic: “As for weekends…”
→ Implies a contrast with other times:
- (On weekdays I work, but as for weekends, I play sports.)

So:

X に – marks time point.
X は – makes X the topic, often with a contrastive feeling.

How do I know if 友達 means “friend” or “friends”? There’s no plural.

Japanese usually doesn’t mark plural on nouns the way English does.

友達 can mean:
- “a friend”
- “friends”
- “my friend(s)”
- in general, “friend(s)”

Context tells you whether it’s one friend or many. Often it doesn’t matter.

If you really need to emphasise plurality, you can say:

友達たち (sounds like “my group of friends”; has a nuance, not just a neutral plural)
たくさんの友達 – many friends
二人の友達 – two friends

In your sentence, 友達と一緒に is naturally understood as “with (my) friend(s)” without specifying how many.

Why doesn’t Japanese use words like “a / the” before 公園? How do I know if it’s “a park” or “the park”?

Japanese has no articles like “a, an, the”.

公園 can be:
- “a park”
- “the park”
- simply “park”

Context decides which English article is best:

If you’re talking about your usual park: “the park”
If you’re introducing the idea of some park: “a park”

Japanese often leaves this kind of specificity unstated unless it’s important.

How flexible is the word order? Can I move things like 週末に or 公園で around?

Japanese word order is fairly flexible, as long as:

The verb stays at the end.
The particles stay attached to the words they mark.

All of these are grammatical (with slight changes in emphasis):

私は週末に友達と一緒に公園でスポーツをします。
私は友達と一緒に週末に公園でスポーツをします。
私は公園で週末に友達と一緒にスポーツをします。

Natural, neutral order often puts time earlier, then place, then action: > (私は) 週末に公園で友達と一緒にスポーツをします。

As a learner, it’s safe to stick close to that pattern.