Learn Italian: L'orchestra che suona stasera è famosa. - The orchestra that plays tonight is famous.

In Italian, collective nouns that refer to a group of people, like l'orchestra, la gente, or la famiglia, are strictly singular in grammar. You must use singular verbs like suona and è because the grammatical subject is one single entity, regardless of how many people are inside it.

Why does the adjective famosa end in -a instead of a plural ending?

Just like the verbs, any adjective describing a collective noun must agree with the grammar of the noun, not the number of people in the group. Since l'orchestra is a feminine singular noun, the adjective must be the feminine singular famosa.

Could I use gioca instead of suona for playing in this sentence?

No, because Italian has two different verbs for playing. You must use suonare for playing music, an instrument, or ringing a bell. Giocare is strictly used for playing sports, playing a game, or playing like a child.

Why is the relative pronoun che used here instead of cui?