a stolen base; an instance in which a base runner advances safely during the delivery of a pitch (without the help of a hit or walk or passed ball or wild pitch)
steal a base
move stealthily; "The ship slipped away in the darkness"
take without the owner's consent; "Someone stole my wallet on the train"; "This author stole entire paragraphs from my dissertation"
(often followed by `of') not knowing or expecting; not thinking likely; "an unsuspecting victim"; "unsuspecting (or unaware) of the fact that I would one day be their leader"
not suspicious; "deceiving the unsuspecting public"