Another theory on Amon.
In episode 4 there is a a flash back where we see the characters from the past series as adults.
What if Amon is the mystery man from the flashback, he hates benders because Aang took away his bending. Since then he has been trying to find a way to remove others bending. He has not found a way as powerful as Aang’s instead he is able to block their chi in a way that appears to be permanent. The connection between Amon and the flashback could be due to the fact that Korra possesses all of Aang’s memories and Amon could have triggered one of them when he hit her.
Also, Amon’s story is eerily similar to Mako’s ever notice that? It is totally unrelated because his ability to bend would have been taken away by that point but it is interesting.
If you want to read more crazy theories check out my theory on how Amon could be Tenzin. http://jack-west.tumblr.com/post/22003161663
Note: I am not saying that Amon is Tenzin, those are just some reasons why it could be a possibility.