Learn Polish: Tu nie ma żadnego ryzyka.

Because the phrase nie ma (there is not) forces the noun and its describing words into the Genitive case. The dictionary form for risk is ryzyko, which is a neuter noun. The neuter Genitive form of the negative determiner żaden is żadnego.

Why are there two negatives (nie and żadnego) in this sentence?

Polish uses double negation. Whenever you use a negative word like żadnego (not any / no), you must also make the main verb negative by adding nie. A word-for-word translation is literally 'Here is not no risk.'

Why does the sentence use nie ma instead of nie jest for 'there is no'?

When talking about existence or presence ('there is' or 'there are'), Polish uses jest or są. However, the negative version ('there is not' or 'there are not') is a special exception: it is always nie ma.

Why does the word for risk end in '-a' (ryzyka)?

The basic dictionary form is ryzyko. Because it ends in '-o', it is a neuter noun. It changes its ending to '-a' here because the verb phrase nie ma always requires the noun that follows it to take the Genitive case.