In a small saucepan combine beer, onion, catsup, sugar, Worcestershire sauce, lemon juice, paprika, chili powder, and pepper. Bring to boiling, reduce heat. Simmer, uncovered, for 5 minutes. Cool.
Use a sharp knife to score steaks on both sides. Place steaks in a plastic bag set inside a deep bowl. Pour marinade over steaks. Seal bag and turn steaks to coat. Marinate in the refrigerator for at least 1 hour or up to 24 hours.
Remove steaks from bag; reserve marinade. Place steaks on grill rack of an uncovered grill directly over medium-hot coals. Grill steaks, uncovered, for 12 to 15 minutes for medium (160 degrees F) doneness; turning the meat halfway through grilling.
Meanwhile, place reserved marinade in a small saucepan; bring to a full boil. Cook and stir for 1 to 2 minutes. Serve with steaks. Makes 6 servings.