When dealing with a "check airman" you should be dealing with a highly professional and very standard individual. If they are resorting to physical violence or even oral abuse he should be reported and be stripped on his/her check airman status. I would never encourage fighting in the cockpit but I don't know how to react if someone purposely hit me in the cockpit. Not cool either way. Call your ALPA rep and get in touch with your union part of professional standards.