 Each level of play has different specifications for the size and shape of the key : in American leagues , where the basketball court is measured in imperial units , the shape is rectangular , while in FIBA @-@ sanctioned events , which use the metric system , the shape was trapezoidal , before being changed to a <unk> as well . In addition to the <unk> <unk> , the key includes a free @-@ throw circle at its " head " or " top " . 
