Veteran center Bob Hallen, thrust into Cleveland's starting lineup to replace injured Pro Bowler LeCharles Bentley, will announce his retirement on Friday because of a back injury. "The possibility of him coming back is pretty much eliminated because he is in the process of faxing a retirement letter," Browns coach Romeo Crennel said after Cleveland's 20-7 preseason loss to Philadelphia on Thursday night. "He has decided to move on and that's what we're going to do."