The last two years , Derrick Burgess has been the Raiders ' most productive defensive lineman . But with a lingering calf injury that began nearly a month ago , the Pro Bowl end is lucky just to get on the practice field . He 's not the only Oakland defensive lineman hurting , either .
According to the above context, answer the following question.
Why has the Raiders defensive line not been firing on all cylinders ?


They have an injured player .