noun-modifying (irregular)
Describes a person with strong, unwavering spirit; often used for someone who stays calm under pressure. Functions as a prenominal modifier.
He is a fearless man.
Only a gutsy player can stay calm in that situation.
From 根性 (こんじょう, 'willpower, guts') + の + past form of 据わる (すわる, 'to settle, to be steady'). Literally 'with settled guts', meaning someone whose spirit is firmly grounded.