Блиц-раунд начинается, и секундомер работает.

Блиц-раунд is a compound noun borrowed from other languages: блиц means blitz / rapid, and раунд means round. In Russian, some compound nouns like this are written with a hyphen, especially newer borrowed combinations.

Both parts together function as one masculine noun:

• блиц-раунд начинается
• после блиц-раунда
• в блиц-раунде

So you should learn блиц-раунд as a single vocabulary item.

It is in the nominative case because it is the subject of the verb начинается.

In this sentence:

• блиц-раунд = the thing that begins
• секундомер = the thing that is running / operating

Both nouns are subjects, so both are nominative singular.

Because the verb here is начинаться, not начинать.

• начинать / начать = to begin something, to start something
• начинаться / начаться = to begin, to start (about the event itself)

So:

• Я начинаю урок. = I begin the lesson.
• Урок начинается. = The lesson begins.

In your sentence, the blitz round itself is beginning, so Russian uses начинается.

The -ся ending often marks a reflexive verb, but in many cases it does not literally mean someone is doing something to themselves. Very often it creates an intransitive verb.

Here:

• начинать = to start something
• начинаться = to start / to begin

So -ся helps turn the verb into the version used when the subject is the thing undergoing the action.

A useful way to think about it:

• начинать = to begin something
• начинаться = to begin

In Russian, the present tense of an imperfective verb can mean:

• something happening now,
• something in progress,
• or something just about to happen / regularly happening.

So Блиц-раунд начинается can mean:

• The blitz round is beginning
• The blitz round begins

This is very natural in Russian for events, announcements, and live situations.

Yes, but the meaning shifts slightly.

• начинается = is beginning / begins
• начнётся = will begin

So:

• Блиц-раунд начинается sounds like it is starting now, or is just beginning.
• Блиц-раунд начнётся sounds more clearly future: The blitz round will begin.

In a live setting, начинается is very natural.

In Russian, работать is often used for machines, devices, and systems to mean:

• to work
• to function
• to be running / operating

A секундомер is a stopwatch, so секундомер работает means it is operating or running.

You may also hear other expressions in different contexts, but работает is perfectly normal for a device.

Examples:

• Телефон не работает. = The phone isn’t working.
• Часы работают. = The clock is running.
• Секундомер работает. = The stopwatch is running.

Because the subject секундомер is:

• third person
• singular
• masculine noun

The dictionary form is работать. In the present tense:

• я работаю
• ты работаешь
• он / она / оно работает
• мы работаем
• вы работаете
• они работают

Since секундомер is like он, you get работает.

Yes. Секундомер is a masculine noun.

You can tell because it ends in a consonant in its dictionary form, which is very often masculine in Russian.

That is why you would say:

• новый секундомер
• этот секундомер
• секундомер работает

Because this sentence joins two full clauses:

• Блиц-раунд начинается
• секундомер работает

Each part has its own subject and verb, so Russian normally uses a comma before и when connecting them.

This is similar to English:

• The blitz round begins, and the stopwatch is running.

Yes. Russian word order is flexible, although the original version is the most neutral.

Neutral:

• Блиц-раунд начинается, и секундомер работает.

Other possible orders can shift emphasis:

• Начинается блиц-раунд, и работает секундомер.
• Секундомер работает, и блиц-раунд начинается.

These alternatives are grammatically possible, but they may sound more marked or stylistically specific. For a learner, the original order is the safest and most natural.

A natural stressed version is:

• блиц-рáунд начинáется, и секундомéр рабóтает

Stress matters in Russian, so it is useful to learn the words with stress:

• блиц-рáунд
• начинáется
• секундомéр
• рабóтает

A rough pronunciation guide:

• blits-ROUND
• na-chee-NA-yet-sya
• see-koon-da-MYOR
• ra-BO-ta-yet

It is used in Russian, but it is a borrowed expression. Russian often uses borrowed words for games, competitions, sports, media, and modern formats.

So even though it is not originally Slavic, it is still a normal Russian noun and behaves like one grammatically.

It can mean either, depending on context. Russian present tense often covers both ideas.

So секундомер работает can be understood as:

• the stopwatch works
• the stopwatch is working
• the stopwatch is running

In this specific sentence, because the blitz round is beginning, the most natural interpretation is the stopwatch is running.