Would it be Sports are an essential part to every high school or would it be Sports is?

Answer 1

Is it more than one sport? If so, "are" is correct. "Is" is singular. "He is..." "They are..."

Answer 2

Sports are -- high schools usually have several sports.

Answer 3

Note that "sports" is not usually capitalized unless it's at the beginning of a sentence or part of an official name, like "ABC Sports".