健はフットボールの選手です。

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

football (incl. soccer, rugby, American football, etc.; esp. used for soccer)

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

player (in game); team member

be; is