Usage patterns
〈人〉が闘志を抱くto harbor fighting spirit
He quietly harbored a fighting spirit.
闘志が湧くfighting spirit wells up
The opponent's taunt made my fighting spirit well up.
闘志をむき出しにするto openly display one's fighting spirit
The players fought with their fighting spirit fully on display.
闘志を失うto lose one's fighting spirit
After a losing streak, he lost his fighting spirit.
Expressions
闘志を燃やすburn with fighting spirit; be fiercely competitive