http://www.narutobase.net/manga/Naruto/613/4
Here Shikaku states that the speciality of the three clans (Yamanaka, Nara, Akimichi) is to block. The only thing is they don't have enough chakra to hold the juubi down.
http://www.narutobase.net/manga/Naruto/613/5
Here he asks Kakashi about the...