A defending player who stays close to an opponent in order to mark them.
(dated) A player employed by a private club and available to compete against members.
A gene or DNA sequence with a known location on a chromosome that can be used to identify individuals or species.
(In competition law) A recognition given by a competition authority that a company is the first to approach it to reveal the existence of a cartel, as a prelude to a formal application for leniency for the company.