What was once one of mixed martial arts great “what if” matchups will become a reality in a different type of combat on Oct. 15.Japanese promotion Rizin announced Friday that Frank Shamrock and Kazushi Sakuraba will square off in a grappling match on its Oct. 15 card at Marine Messe Fukuoka in Fukuoka, Japan. Shamrock is stepping in as a replacement for Dan Henderson , who withdrew from the match due to an injured neck.Rizin “Aki No Jin” will also feature the “B” portion of the bantamweight grand prix and the opening round of the women’s super atomweight grand prix.Shamrock, a former UFC champion, once called out Sakuraba at a Pride Fighting Championships event, but the bout never came to fruition. At the time, Sakuraba was one of the sport’s biggest stars in Japan.The 48-year-old Sakuraba has competed in grappling matches against Renzo Gracie in 2014 and in a tandem match with Hideo Tokoro against Wanderlei Silva and Kiyoshi Tamura at a Rizin event in 2016. Both bouts ended in a draw. Shamrock, 44, last fought MMA in 2009, losing to Nick Diaz via second-round TKO under the Strikeforce banner. He last grappled against Henderson in 1997, winning via submission.Shamrock and Sakuraba will compete in a 15-minute bout with no point system, which means the match will either end in a submission or as a draw.