"The All-Ireland Final is played in Croke Park."
Translation:Imrítear Cluiche Ceannais na hÉireann i bPáirc an Chrócaigh.
Presuming that it’s not a transpositional typographical error, it could be because páirc is feminine, Páirc an Chrócaigh makes both páirc and Crócach definite, and an becomes na for definite feminine genitive nouns. I hadn’t previously considered what would happen to the article in a situation where a definite genitive noun phrase had its governing noun feminine and its governed noun masculine.
EDIT: It’s a transpositional typographical error. The 2012 Caighdeán provides a mixed example (§1.4, page 25), bun na sráide (“the bottom of the street”), where the article takes the appropriate form for the (feminine) governed noun sráid rather than for the (masculine) governing noun bun.
Throughout the history of Irish, gender of the genitive article has always been decided by the governed noun.