Place roast in a Dutch oven, and sprinkle with chopped onions. Cover with tomatoes, water, sugar and Worcestershire sauce. Season with salt and pepper.
Cook over medium heat with lid slightly ajar for 3 hours.
Remove meat, and shred with 2 forks. Discard bones, fat and gristle. place shredded meat back into sauce, and cook until liquid is reduced, 15 to 20 minutes.
