Answer
The culprit responsible for the unfortunate incident that resulted in Hardcore Holly's neck injury was none other than the formidable Brock Lesnar. During a high-stakes match in 2002, Lesnar unleashed his devastating finishing move, the F-5, with tremendous force, leading to the agonizing injury that sidelined Hardcore Holly for a significant period. This occurrence stands as a stark reminder of the physical risks and demanding nature of professional wrestling.