kare ha tiimusen ni sankasitagatte iru.

Because Japanese usually avoids stating another person’s inner feelings directly with 〜たい.

• 〜たい is most natural for your own desire:
  • チーム戦に参加したい。 = I want to participate in the team match.
• For a third person, Japanese commonly uses 〜たがる / 〜たがっている:
  • 彼はチーム戦に参加したがっている。 = He wants to participate in the team match / He seems eager to participate.

So 〜たがっている often implies that the speaker is judging this from the person’s behavior, attitude, or words.

〜たがっている is the ている form of 〜たがる, which means to show signs of wanting to do something.

Structure:

• verb stem + たがる
• then たがっている for an ongoing state

In this sentence:

• 参加する = to participate
• 参加したがる = to show a desire to participate
• 参加したがっている = is currently showing that desire / wants to participate

So the nuance is slightly more observational than plain English wants to.

No. This is a very common point of confusion.

It is not:

• 参加した
  • がっている

It is:

• 参加し
  • たがる
    • ている

So the breakdown is:

• 参加する
• stem: 参加し
• add たがる → 参加したがる
• te-form: 参加したがって
• plus いる → 参加したがっている

It only looks like 参加した at first glance, but here した is part of したがる, not the past tense of する.

Because 参加する normally takes に to mark what you participate in.

Examples:

• 試合に参加する = participate in a match
• 会議に参加する = participate in a meeting
• チーム戦に参加する = participate in a team match/event

Here, に marks the target event or activity that someone joins.

Because 参加する does not usually take a direct object with を in this meaning.

Japanese says:

• イベントに参加する
• 大会に参加する

not usually:

• イベントを参加する

So even though English says participate in and not just join to, Japanese uses に with 参加する.

チーム戦 means a team match, team competition, or team-based event.

It is made of:

• チーム = team
• 戦 = match / battle / contest

So it refers to a format where people compete as teams, not individually.

Depending on context, it could mean:

• a team match in sports
• a team battle in games
• a team-based competition more generally

The sentence is read:

かれ は チームせん に さんかしたがっている。

Word by word:

• 彼 = かれ
• チーム戦 = チームせん
• 参加 = さんか

Normally, Japanese would be written without spaces:

彼はチーム戦に参加したがっている。

は marks 彼 as the topic of the sentence.

So 彼は means something like:

• as for him
• he

The sentence is then saying something about him: namely, that he wants to participate in the team event.

If you used が instead, the nuance would change a bit:

• 彼がチーム戦に参加したがっている。

That version puts more focus on him as the person who wants to participate, perhaps in contrast to someone else.

Normally, no.

For your own desire, you would usually say:

• チーム戦に参加したい。 = I want to participate in the team match.

For someone else:

• 彼はチーム戦に参加したがっている。 = He wants to participate.

This is because Japanese treats another person’s desires as something you usually observe from the outside, rather than state directly as a fact.

The いる is part of 〜ている, which often describes an ongoing state.

So:

• 参加したがる can sound more general, like shows a tendency to want to participate
• 参加したがっている means is currently showing that desire

In natural English, both may be translated as wants to participate, but 〜ている helps express that the desire is presently visible or active.