to stain, to dirty, to tarnish
No quería manchar su expediente con una acusación.
He didn't want to tarnish his record with an accusation.
— Cuestión De Honor (1992)
Ella se ha quitado las botas, para no manchar con sangre la piel.
She has taken off her boots, so as not to stain her skin with blood.
— Señora venganza (2005)
El honor del Emperador no se puede manchar.
The Emperor's honor cannot be tarnished.
— El último emperador (1987)