NORMAN, OK – SEPTEMBER 08: A member of the Oklahoma Sooners spirit squad celebrates a touchdown against the UCLA Bruins at Gaylord Family Oklahoma Memorial Stadium on September 8, 2018 in Norman, Oklahoma. The Sooners defeated the Bruins 49-21. (Photo by Brett Deering/Getty Images)The Oklahoma Sooners got a bit of a surprise this week when incoming freshman defensive tackle Derek Green abruptly announced his plan to withdraw. But now we know what the reason was that led Green to make the decision.Coming out of high school, 247Sports had Green rated as the No. 721 prospect in the country. He was considered the No. 57 defensive tackle prospect, and the No. 32 prospect from the state of North Carolina.According to Bob Przybylo of SoonerScoop, Green plans to enter the military instead of playing football. Green added the caveat that he would enter the transfer portal if he ultimately changed his mind.Przybylo tweeted his quote, with a link to a paywalled Rivals article: “I am planning to go serve our country proudly and hit the portal if I change my mind.” – #Sooners incoming freshman DL Derek Green, announcing he is leaving #OU. @JLMcCuistion has a lot more info, too, right here: ($) https://t.co/pTELr3SldS— Bob Przybylo (@BPrzybylo) February 13, 2019The announcement came just a week after Green had enrolled at Oklahoma.247Sports’ OUInsider would later pick up the story, revealing that Green intends to join the U.S. Navy.He would go on to say that he didn’t want to “waste anybody’s time” in announcing the decision to leave quickly.“I don’t want to waste anybody’s time,” Green told OUInsider, “because Oklahoma has a great group of guys on that defense that’s there and coming in and I want them to be successful and they can spend more time developing them while I try to serve my country.”Unfortunately for the Oklahoma Sooners, Green’s departure does leave the team in something of a bind at his position.Green was the only defensive tackle that the team had recruited in the Class of 2019.He also happens to be the second defensive lineman that has left the school, with defensive end Ron Tatum reportedly transferring as well.With Green and Tatum leaving, the depth at Oklahoma’s defensive line is getting thinner heading into 2019.