Ben Shapiro vs Neil deGrasse Tyson: The WAR Over Transgender Issues

[Ferrocyanide]

It depends on how you define morality.
If you define morality as = causing harm is immoral.

That's not how morality is defined:

Morality 
noun
1. principles concerning the distinction between right and wrong or good and bad behaviour.

Ultimately all moral assertions rest on subjective opinion. 

If you define morality as = causing harm is immoral.

Then, if person X punches person Y, person X is causing harm. He did an immoral act.

This is still a subjective assertion, all you have done is use a begging the question fallacy to assume your conclusion in your opening premise, it is both arbitrary and circular. Also moral assertions are relative, what if you punched someone for example, to prevent a greater harm, like murder or rape? 

Note the notion causing harm is immoral is a subjective one, not an objective one.

I think your definition doesn't work either. I didn't see anything circular reasoning in it or any begging but you said principles, which is unclear.
You said good and bad behavior but you did not display the logic behind it.
What logic should I use to figure out if something is right or wrong?

I can also make up words and give them vague definitions:
Kazouting and "to kazout" = spending the day doing certain things in a full way.

I think that if we use emotions as our guide, then this issue of "morality is fully subjective" gets changed to "morality is partially objective".
It is an objective fact that humans have pain sensors. You can punch a human in the face and activate the pain sensors.
You can also do psychological harm using verbal abuse and other methods.

Isn't morality mostly derived from feelings, from pain?

Also moral assertions are relative, what if you punched someone for example, to prevent a greater harm, like murder or rape?

It all comes down to "how do you want to define morality?"

I'll be happy to answer your question:
In your above example, the focus seems to be on rape. That is the initial action. That is the problem point.
In order to stop it, you want to take an immoral action ==> punch someone.

The rape part, we can judge that it is an immoral act. it is objectively immoral.
The punching part, we would have to decide as a society if this action is acceptable. This is the subjective part.
It is similar to a sheet of glass cracking. The crack is spreading. You try to stop the crack by cutting the glass at some point. Did you make the best decision possible?