What crime did hagrid comitte in his time at hogwartz?

During his time at Hogwarts, Hagrid committed the crime of illegally bringing a dragon to the school. In "Harry Potter and the Sorcerer's Stone," he was found to have a baby Norwegian Ridgeback dragon, which is forbidden by wizarding law. This act led to his expulsion from Hogwarts, although he later returned to the school as the Keeper of Keys and Grounds.