underhand

with hand brought forward and up from below shoulder level

• “an underhand pitch”
• “an underhand stroke”

marked by deception

• “achieved success in business only by underhand methods”

slyly and secretly

• “Mean revenge, committed underhand” John Donne
• “oldline aristocratic diplomats underhandedly undermined the attempt...to align Germany with the Western democracies” C.G.Bowers

with the hand swung below shoulder level''

• “throwing a ball underarm”