How does drawing then discarding work with a full hand?
No, if you cast that spell on your opponent, he draws 2 for a total of 9 hand cards, then discards 4 cards, down to 5.


  402.2. Each player has a maximum hand size, which is normally seven cards. A player may have any number of cards in his or her hand, but as part of his or her cleanup step, the player must discard excess cards down to the maximum hand size.


The cleanup step is the last step in each player's turn.