Is assault against the first precept? The first precept states


  I undertake the training rule to abstain from killing.


So does this mean that punching someone in the nose isn't actually against the first precept and the five precepts generally. It really feels like it should be.
The following five conditions must be satisfied to break the first precept.


The being must be alive.
There must be knowledge that it is a living being
There must be intention to cause its death
Action must be taken to cause its death
Death must result from such action


So punching someone in the nose does not break the 1st precept. But it weakens it. Since the question is if it's against(not if it breaks) the precept, the answer is yes.

Weakening here means the merits you acquire by keeping to first precept are reduced or weakened. Also, when it comes to the consequences of Kamma, Killing results in one having a short life span if born as a human again. Just injuring or torturing results in having bad health if born as a human again. killing usually involves inflicting pain or torturing as well. So it can result in bad health too.