The Cowboys’ defense suffered another blow when backup safety Jakar Hamilton was slapped with a four-game suspension for violating the substance abuse policy.Hamilton admitted it was a mistake and was apologetic after Thursday’s game, although he didn’t reveal too many specifics into his situation. He said he missed a scheduled drug test during OTAs, which counts as a failed drug test under league policy.A four-game suspension means Hamilton has violated the drug policy twice and is subject to unannounced testing up to 10 times a month. Another failed test could result in a one-year suspension.Hamilton declined to say what he tested positive for previously.“I just owned up to it,” Hamilton said. “It’s not heartbreaking for me, but a learning experience. It’s a great opportunity for me to be humbled and to take this as a lesson learned.”Hamilton hopes his situation can help educate other players to avoid the same mistake. Owner Jerry Jones is also of the belief that this will help Hamilton continue to mature and become a better person.Asked if Hamilton’s suspension puts his roster spot in jeopardy, Jones said: “I want to look at how we do his status because we think he has potential. I don’t want to comment one way or the other on his [status], but we have thought he does some really good things in there and we’ll be looking at his status as to how it affects what we’re trying to do with our numbers and players we want to keep.”Hamilton will be eligible to return Sept. 29 after the game against the New Orleans Saints, according to an NFL spokesman.Hamilton, who signed as an undrafted free agent out of South Carolina State last year, has had a solid training camp. Injuries, though, have limited to him just one preseason game. He did not play Thursday.He becomes the second defensive back to receive a four-game suspension. Cornerback Orlando Scandrick violated the league’s policy on performance-enhancing drugs after taking a street drug known as “molly,” which contained amphetamines.