Suppose Player 1 has a Dragon on the table and Unsummon in hand, while Player 2 has two Spiders on the table.
Player 1 chooses to attack with the Dragon and Player 2 chooses to block with one of the Spiders. Before damage has been put on the stack (Note: as of the 2010 MtG rules update, combat damage is a turn-based action that doesn't use the stack.) Player 1 uses Unsummon on the blocking Spider.
Does Player 2 take any life damage from the attacking Dragon?