Trim any fat from pork. Place the pork in a plastic bag set in a shallow dish. For the marinade, in a small bowl combine peach nectar, teriyaki sauce, rosemary, and olive oil. Pour over pork. Close bag. Marinate in refrigerator for 4 to 24 hours, turning bag occasionally. Drain the pork, discarding marinade.
In a grill with a cover arrange preheated coals around a drip pan. Test for medium heat above the pan. Place pork on grill rack directly over the drip pan. Cover and grill about 30 minutes or until no pink remains and the juices run clear.