This is a slang term used to describe a player who shows off excessively. A more flamboyant player is often called a "hot dog", in reference to elaborate celebrations or other showy tactics.
There are many instances in which a player could be called a "hot dog", all of which relate to showing off. An example would be if a player decided to use one hand on an otherwise routine catch. The players who most commonly earn this designation are wide receivers, as this position tends to be one associated with flamboyant players. Players who would fit this description include Terrell Owens and Chad Ochocinco.