In an underhanded manner.

simple past tense and past participle of underhand

Done by moving the hand (and arm) from below. / Sly, dishonest, corrupt, cheating. / Insincere; sarcastic. / Secret; surreptitious. / Understaffed.

Devious people, collectively.

To toss or lob with an underhand movement. / To trick, deceive or gull. / (mining) To excavate downward in successive steps or horizontal slices while positioned above on unbroken ore.

secret; clandestine / (by extension) dishonest and sneaky; done in a secret or sly manner / (in various ball games, of a ball) thrown (etc.) with the hand brought forward and up from below

with an underhand movement / in a sly, sneaky or secret manner

(textiles) The lower of two hands, the hand under the work.

plural of underhander

A ball thrown or bowled underhand. / One who throws or bowls a ball underhand. / One whose personality inclines toward taking revenge by underhand means.