tugi ha supea desita.

Because は is being used as the topic particle, and when は is a particle, it is pronounced wa.

So in this sentence:

• 次 = next
• は = topic marker, pronounced wa

This is one of the first pronunciation exceptions learners meet in Japanese.

次 means next or the next one.

It is usually read つぎ (tsugi).

In a sentence like this, 次 often refers to whatever comes next in the current context, such as:

• the next turn
• the next frame
• the next try
• the next item/event

Japanese often leaves that specific noun unstated if it is already understood from the situation.

は marks 次 as the topic of the sentence.

So 次は means something like:

• as for the next one
• the next one, ...

The rest of the sentence says something about that topic:

• スペアでした = was a spare

So the structure is:

• Topic + comment

That is a very common Japanese sentence pattern.

スペア is a loanword from English spare, so it is written in katakana, which is the script commonly used for:

• foreign loanwords
• foreign names
• sound effects
• emphasis in some cases

In this context, スペア most likely means a spare in bowling.

Not always. Loanwords in Japanese often have meanings that are narrower or slightly different from the original English word.

Here, スペア most naturally means a bowling spare.

In other contexts, spare in English can mean things like:

• extra
• unused
• replacement

Japanese may use other words for those meanings depending on the situation. So in this sentence, the bowling meaning is the most likely one.

でした is the past polite form of です.

So:

• です = is / am / are
• でした = was / were

Since the sentence is talking about a result in the past, でした is used.

Pattern:

• A は B です = A is B
• A は B でした = A was B

So 次はスペアでした follows a very basic copula pattern.

Because です / でした can follow nouns and na-adjectives to make polite statements.

Here, スペア is a noun, and でした acts like the polite past copula.

So:

• スペアです = it is a spare
• スペアでした = it was a spare

This is different from verbs, which change form themselves. A noun does not conjugate, so です / でした carries the tense and politeness.

Yes, very likely.

Japanese often omits words that are obvious from context. In English, you might expect something more explicit, such as:

• The next frame was a spare.
• My next shot was a spare.
• The next one was a spare.

In Japanese, if everyone already knows what 次 refers to, there is no need to say the full noun.

This kind of omission is extremely common and natural.

Japanese does not require an explicit subject in every sentence the way English often does.

If the context already makes it clear who or what is being discussed, Japanese usually leaves it out.

So instead of saying something like:

• My next frame was a spare

Japanese can simply say:

• 次はスペアでした

The listener fills in the missing details from the situation.

It would be similar, but not exactly the same in nuance.

• 次はスペアでした: As for the next one, it was a spare.
• 次がスペアでした: The next one was the one that was a spare.

So:

• は gives a topic, often with a contrastive or descriptive feel
• が identifies or focuses on the subject more directly

In many contexts, 次はスペアでした sounds more natural if you are simply narrating a sequence of events.

Normally, standard Japanese is written without spaces.

So the usual written form would be:

次はスペアでした。

Spaces are often added in teaching materials to help beginners see the parts of the sentence more easily.

So the spaced version is learner-friendly, but not normal everyday Japanese spelling.

The pattern is:

X は Y でした

meaning:

As for X, it was Y

In this sentence:

• X = 次
• Y = スペア

So the grammar is very straightforward:

• topic
• noun predicate
• polite past copula

This is one of the most useful basic patterns in Japanese.

It is polite, but not especially formal.

The politeness comes from でした.

Compare:

• 次はスペアでした。 = polite
• 次はスペアだった。 = plain/casual

So this sentence would be fine in normal polite conversation, narration, or explanation.