Punching both Basim and Sigurd will lower your loyalty with Sigurd and affect the ending. If you choose not to punch Basim or Sigurd then your loyalty will stay the same.

Does punching Sigurd count as a strike?

Who to punch? During the Oxenfordscire arc, Eivor gets into a heated argument with Sigurd and Basim. During the argument, Eivor is given dialogue options of “Take Breath”,”Punch Basim”,”Enough of This” and “Punch Sigurd”. If Eivor punches either Sigurd or Basim then that counts as a Sigurd Strike.

Should I punch Sigurd or take a breath?

Like with Styrbjorn's resources when you left Norway, this is one of the times where your differences with Sigurd come to a head, and he will remember the outcome when it comes to decision making later. So with that said, if you can stand it, you should take a breath and not punch Basim or Sigurd.