What's wrong with collaboratively working together? Why is there a need to create an atificial competition between a "offence" and a "defence" team?

And why should team members be collaborative amongst their team? E.g. why should the "offence" team members suddenly help each other if it's not happening generally?

This sounds a lot like JDD - Jock Driven Development.

Perhaps the underlying problems of "don't touch it because we don't understand it" should be solved before engaging in fake competition to increase the stress levels.