Learn Arabic (Modern Standard): الفريق رقم عشرة ممتاز.

Because we are not counting teams here (as in "ten teams"), but using the number as a label or ID. When reciting numbers on their own or using them as labels after the word رقم (number), Arabic uses their default "bare counting" form. For numbers 3 to 10, this default form ends with the feminine marker ة.

Why do we say الفريق (the team) when the English translation just says "Team number ten"?

In English, we often drop "the" when giving something a title or number (like "Room 5" or "Team 10"). In Arabic, because we are talking about a specific, known team, we must keep the definite article ال (the) attached to الفريق.

Where is the word for "is" in this sentence?

Arabic doesn't use a word for "is" or "are" in the present tense. You simply state the subject, الفريق رقم عشرة (the team number ten), followed directly by the description, ممتاز (excellent). Putting them side-by-side automatically creates the meaning "is excellent".

Why doesn't ممتاز (excellent) have a feminine ending to match عشرة (ten)?

Because ممتاز describes الفريق (the team), which is a masculine word. The phrase رقم عشرة just helps identify which team we mean. Since the main subject is masculine, its description ممتاز must be masculine too.