"Fight mode" refers to a state of heightened alertness and readiness to combat or defend oneself against a threat or challenge. It implies being mentally and emotionally prepared to engage in a physical or metaphorical battle. Full definition
If you're in fight mode, then say something. (inc.com)
If you're sure you're right and the other person's wrong, you're already moving into fight mode, where your child looks like the enemy. (psychologytoday.com)
There is a single fight mode where you can choose to fight against a CPU opponent of your choosing along with whichever difficulty you choose. (gamerstemple.com)