No rule for this one
No ending or word group predicts the article of Hobby. Learn it as a pair and say it out loud: das Hobby.
das Hobby
It's das Hobby. Hobby is neuter, plural die Hobbys.
Mein Hobby ist Kricket.
My hobby is cricket.
No ending or word group predicts the article of Hobby. Learn it as a pair and say it out loud: das Hobby.