kono toukyuu ha ii.

この means this, but it must be followed by a noun.

So:

• この投球 = this pitch / this throw
• この cannot stand by itself
• if you want to say this by itself, you would use これ

Compare:

• この投球はいい。 = This pitch is good.
• これはいい。 = This is good.

A very common beginner mistake is trying to use この alone. In Japanese, この / その / あの must directly modify a noun.

投球 literally refers to a thrown ball, a pitch, or pitching, especially in a baseball context.

Depending on context, it can mean:

• a single pitch
• the act/style of pitching
• a thrown ball in sports discussion

So この投球はいい。 most naturally sounds like something said while evaluating a baseball pitch or a pitcher’s throw.

For everyday throwing in a non-sports context, Japanese might use other words depending on the situation. 投球 sounds fairly sports-related.

は marks the topic.

So この投球はいい。 is literally something like:

• As for this pitch, it’s good.

In natural English, we usually just say:

• This pitch is good.

The important point is that は does not simply equal English is. It marks what the sentence is about.

Here, the speaker is taking この投球 as the topic and then making a comment about it: いい.

Yes, but it changes the nuance.

• この投球はいい。 = This pitch is good. / As for this pitch, it’s good.
• この投球がいい。 = This pitch is the good one / I prefer this pitch / This is the one that’s good.

Very roughly:

• は often presents something as the topic for comment
• が often gives stronger focus to that specific thing

So if someone is comparing several pitches, この投球がいい。 can sound more like this one is the good one.

Because this sentence is in plain style.

• この投球はいい。 = plain/casual style
• この投球はいいです。 = polite style

Both are grammatically correct.

Japanese often omits です in plain statements when the predicate is an -i adjective like いい, 高い, 速い, etc.

So:

• この投球は速い。
• この投球はいい。

are complete sentences already.

いい is the common everyday form of よい.

Both mean good.

• いい = more common in ordinary speech
• よい = more formal, stiffer, or stylistically written-sounding in many cases

So:

• この投球はいい。 sounds very natural
• この投球はよい。 is also correct, but sounds more formal or literary

One thing learners should remember is that いい behaves irregularly in some forms because it comes from よい. For example:

• よくない = not good
• not いくない

Yes. いい is an -i adjective.

It is the predicate of the sentence, describing この投球.

Structure:

• この = this
• 投球 = pitch / throw
• は = topic marker
• いい = good

So the whole sentence is basically:

• This pitch is good.

Because いい is an adjective, no extra word like English is is required in plain Japanese.

Yes, especially in a sports or baseball context.

It sounds like something a commentator, coach, or observer might say when evaluating a pitch:

• この投球はいい。 = This pitch is good.

That said, the most natural wording depends on the exact context. For example:

• この球はいい。 can also be natural if talking about the ball/pitch itself
• このピッチングはいい。 might refer more broadly to someone’s pitching

But この投球はいい。 is perfectly understandable and natural in the right setting.

The spaces are usually just for learners.

Normal Japanese writing would be:

• この投球はいい。

Japanese is normally written without spaces between words.

Textbooks and beginner materials often add spaces to make it easier to see the parts of the sentence:

• この / 投球 / は / いい

So the spaced version is helpful for study, but not how Japanese is usually written in real life.