Переигровка началась сразу.

Переигровка is a noun. It is a feminine singular noun, which you can see from the ending -а.

It usually means a replay or rematch in a game, match, or competition — especially when something has to be played again.

It is related to the verb переиграть / переигрывать.

It is in the nominative case because it is the subject of the sentence — the thing that started.

You can test that by asking: What started?
Answer: Переигровка.

The dictionary form is начаться, meaning to begin / to start.

In the past tense, Russian verbs agree with the subject in gender and number:

• начался — masculine singular
• началась — feminine singular
• началось — neuter singular
• начались — plural

Since переигровка is feminine singular, the correct form is началась.

The -сь is the reflexive ending, the same as -ся. After a vowel, Russian often uses -сь instead of -ся.

So:

• начать = to begin something
• начаться = to begin / to start

That means:

• Он начал игру = He started the game
• Игра началась = The game started

In your sentence, началась means started / began.

This is a question of aspect.

• началась is perfective
• начиналась is imperfective

Here, началась presents the start as a single completed event: the replay started.

If you used начиналась, it would sound more like:

• was beginning
• used to begin
• or a background description, depending on context

So Переигровка началась сразу is the normal way to say that the replay started immediately.

Сразу means immediately, right away, or at once.

It is an adverb, and here it tells you how quickly the replay started.

So it modifies the verb началась.

The word order here is neutral and natural:

Переигровка началась сразу.

Russian word order is more flexible than English word order, because endings often show the grammar clearly.

Other orders are possible, for example:

• Сразу началась переигровка.
• Переигровка сразу началась.

These would still mean roughly the same thing, but the emphasis changes a little.
The original sentence sounds straightforward and neutral.

The stress is:

переигро́вка начала́сь сра́зу

A helpful pronunciation guide:

pye-reeg-ROF-ka na-cha-LAS SRA-zu

The most important stress points are:

• переигрóвка
• началáсь
• срáзу