In a state of preparation or good condition to handle a particular situation. We have to make sure we're in fighting form going into this trial.

What does it mean to be in fighting trim?

To be prepared to tackle a situation, often with an emphasis on one's physical strength or readiness. You'll do great in the race—after months of training, you're in fighting trim.

What type of verb is fight?

[transitive, intransitive] fight (something) to try hard to stop, deal with, or oppose something bad to fight racism/corruption/poverty, etc.