Whether you are describing a legal dispute, a sports rivalry, or a treatment fighting an illness, you will need the preposition protiv (against). This preposition always requires the noun, pronoun, or adjective that follows it to be in the genitive case.
Legal Battles
When talking about lawsuits or testifying against someone, use protiv followed by the genitive.
Remember the standard genitive endings: feminine nouns ending in -a change to -e (like tvrtka to tvrtke), while masculine nouns take an -a ending (like muž to muža). Adjectives modifying these nouns must also match the case.
Personal pronouns also take their genitive form. For example, on (he) becomes njega.
Medicine and Health
In Croatian, you describe what symptom or pathogen a medication treats by saying it acts against it. The illness or cause goes into the genitive case.
Sports Matches
In sports, protiv is used to state who a team is competing against. Possessive pronouns like vaš (yours) or svoj (one's own) take the masculine genitive ending -eg or -og to match the masculine noun klub (club), even if the noun itself is implied rather than spoken.