pitcher's misjudgment; mistake pitch
Baseball term for a pitch thrown due to a lapse in judgment, often resulting in a bad outcome. Used in sports commentary and analysis.
That misjudged pitch in that situation decided the game.
The ace pitcher allowed a comeback with an unexpected mistake pitch.
失投 is a more general term for a bad pitch, while 不覚の一投 specifically implies a mental lapse or misjudgment by the pitcher.
Compound of 不覚 (fukaku, 'oversight, failure') + の (no, possessive particle) + 一投 (ittō, 'one pitch'). The phrase is a set expression in baseball contexts.