He wields a large, spiked club. His name may not be Jack as other Yorkshire folklore refers to "Jack in the Green" and more so the name Jack may just be a term for calling the person an unknown male, like John Doe today.
He wields a large, spiked club. His identity may be unclear, as the term "Jack" could be a generic name for an unidentified person, much like how someone might refer to an anonymous individual as "John Doe."