on a human because he is anxious, wants you to do something, or take him somewhere. but leaning is also a symbol of affection to watch out for.
although wanting to play with you is a sign of affection in itself, when your dog brings you his favorite ball, it may also mean he thinks of you as his pack leader. it is true that your pup will often want to play, but sometimes, he just wants to let you know he cares. 