Historical Rules · 1 April 2011
Rule 702.46c
Official source text from the 1 April 2011 Rules release
A ninjutsu ability may be activated only while a creature on the battlefield is unblocked (see rule 509.1h). The creature with ninjutsu is put onto the battlefield unblocked. It will be attacking the same player or planeswalker as the creature that was returned to its owner's hand.