The band made the announcement via their official site last week. Here is what they had to say: We are sorry to say that Mark has had to temporarily leave the Projekt Revolution tour. He threw his back out in Phoenix and went for an MRI. The doctor informed him that he has a herniated disc. We know he is in a lot of pain and would not go home if it was his choice. This injury can lead to permanent back pain if not treated so he is going home for further treatment and rest. We know he is going to return as soon as he is able to.