To describe a person's interests or hobbies, we can use reflexive verbs "занима́ться", "интересова́ться", "увлека́ться". The noun that follow such a verb and indicates an object of a hobby or interests always appears in the Instrumental case and doesn't require the preposition "c.".
ЗАНИМАТЬСЯ (чем?) спортом, иностранным языком, наукой, бизнесом…