knock back = shock, surprise
- His behaviour really knocked me back. I didn 't think he would do that.
- Her words knocked me back. I didn 't think she would say that.
- The news knocked me back. I didn 't expect it.
- The announcement of their divorce really knocked me back. I thought they were happy together.
- I thought she would gladly say "yes", so her refusal knocked me back a little.
- The unexpected information knocked us all back.