Marinate steak. Combine all of the marinade ingredients in a zip top gallon bag or a large lidded container. Submerge the steak in the marinade and press all of the air out of the bag. Massage and turn the bag over several times to ensure the meat is coated. Marinate for 2 hours at least, or overnight for better flavor.
3/4 cup olive oil, 3/4 cup dark brown sugar, 1/4 cup red wine vinegar, 8 cloves garlic, 1 1/2 Tablespoons Worcestershire sauce, 1 Tablespoon salt, 2 teaspoons black pepper, 2 teaspoons red pepper flakes, 2 sprigs fresh rosemary, 1 1 1/2-2 pound beef top round roast
Grill steak. Preheat your grill to 450 degrees F for direct heat cooking. Sear the steak for approximately 4-6 minutes per side, rotating regularly, until the internal temperature reads 130-135 degrees F for medium rare.
Rest and serve. Remove the steaks from the grill and allow to rest for 10 minutes before slicing against the grain and serving. I like to sprinkle with a little more coarse salt and some fresh cracked black pepper right before serving.
Video
Notes
I actually managed to fit two steaks into the marinade, so if you're cooking for more people you don't need to stress about doubling the marinade too.