(1):

(a.) Done, as pitching, with the hand lower than the shoulder, or, as bowling, with the hand lower than elbow.

(2):

(adv.) In an underhand manner; - said of pitching or bowling.

(3):

(adv.) By secret means; in a clandestine manner; hence, by fraud; unfairly.

(4):

(a.) Secret; clandestine; hence, mean; unfair; fraudulent.