A defender tackles an opponent right on the defender's penalty area line in a careless manner. how should the referee restart play

The referee restart play by "Penalty kick".

A penalty kick refers to a technique for restarting play in affiliation football, in which a player is permitted to make a go on the objective or take a shot while it is defended just by the contradicting group's goalkeeper. It is granted when a foul deserving of an immediate free kick is conferred by a player in his or her own particular penalty zone.