Whisk together rub ingredients in a small bowl or jar.
Crumple the strips of foil into balls and place at the bottom of the slow cooker. Pour the beer into the slow cooker. Drop the rosemary into the beer.
Prep the chicken by removing the innards and trimming excess fat. Season chicken with rub, covering both under and above the skin. Put chicken in slow cooker on top of foil, so that it rests above the beer.
Cover and cook until chicken is cooked through so that when the thigh is cut near the bone, the juices run clear. This should take 6 to 8 hours on low, or 4 to 5 hours on high.
Optional: To get crispy skin, transfer the chicken to an oven safe dish and heat under the broiler for 2 to 5 minutes.