How to Make It
Stir together pineapple juice, stock, soy sauce, brown sugar, ketchup, ginger, and garlic in a medium bowl. Reserve 1 cup marinade for basting and drizzling. Place chicken in a large ziplock plastic freezer bag; add remaining marinade. Seal bag, and refrigerate at least 3 hours or up to overnight.
Remove chicken from marinade; discard marinade. Sprinkle chicken with salt. Preheat grill to medium (350°F to 400°F). Place chicken on oiled grates; grill, turning and basting often with 1/2 cup of the reserved marinade, until crispy and a meat thermometer registers 160°F, about 25 to 35 minutes. Transfer chicken to a platter. Baste pineapple slices with some of the remaining marinade; place on oiled grates, and grill, uncovered, until grill marks appear, about 4 minutes per side. Cut pineapple slices as desired. Add to platter, and garnish with scallions. Drizzle with remaining marinade.