Yesterday afternoon, a mob of common grackles arrived in my backyard - 12+ birds. I have several birdfeeders in my yard at Mt. Pleasant & Eglinton, always well attended by sparrows. While watching this massive group , I saw one attack a sparrow! The sparrow had been pecking on the ground and the grackle grabbed it by the neck, sat on it's back and poked at it's neck and back severly with it's beak. This action went on for about a minute, then the sparrow wriggled free and floundered off.
On reading my birding books, I see that grackles do have a 'meat' diet as well as seeds but I've never witnessed this behaviour before. Something unpleasant about a grackle attacking a sparrow vs a hawk taking one of the many pigeons, in my opinion anyway.