Learn Russian: В третьем сезоне они не получили кубок. - In the third season, they did not get the cup.

The ordinal number третий (third) is special. Unlike most ordinal numbers which act like regular hard adjectives, третий has a soft declension pattern. To agree with the masculine prepositional noun сезоне, it becomes третьем.

Why do we use the prepositional case for В третьем сезоне when expressing time?

When expressing time periods like seasons, months, or years with the preposition в, Russian requires the prepositional case. That is why it is в сезоне (in the season) rather than the accusative case, which is reserved for shorter time frames like days of the week.

Why use the perfective verb получили in a negative sentence? I thought negative actions often trigger the imperfective.

While the imperfective is common in negative sentences to show an action was completely absent, the perfective не получили is used here because it focuses on the failure to achieve a specific result. They played the season, but they failed to complete the specific action of getting the trophy.

Shouldn't кубок be in the genitive case because of the negative не?

You can often use the genitive case for a direct object in a negative sentence, but using the accusative case is also perfectly correct and very common for specific, concrete objects. Because кубок (cup or trophy) is masculine and inanimate, its accusative form looks exactly the same as its dictionary form.