defensive

purely

When the team played poorly, their coach adopted a purely defensive strategy to avoid losing.

essentially, largely

The team's strategy was essentially defensive after losing their best striker to injury.

become, get

When I suggested she needed help with the project, she became defensive and refused to listen.

extremely, fiercely, very

When she mentioned his mistake, he became extremely defensive and refused to listen to any criticism.

oddly

When I mentioned her cooking, she became oddly defensive about her recipe choices.

about

She became defensive about her decision when her friends questioned it.