un·der·hand·ed 
(ŭn′dər-hăndĭd)
(ŭn′dər-hăndĭd)adj.
1. Acting or done in a deceptive, secret, or sly manner; dishonest and sneaky. See Synonyms at secret.
2. Underhand: an underhanded toss.
adv.
1. In a sly and secret way.
2. With an underhand movement.
un′der·handed·ly adv.
un′der·handed·ness n.