The term "Player-Manager" is used in footbal to define a manager of a particular football team who also plays for the team or vice-versa. So the person who is the manager of the team is also one of the players of the team.
The situation to appoint a player-manager arises when the manager of the club leaves and there is a vacant position in the managerial office. The club chairman of president usually opts for a caretaker manager under such circumstances but may also ask one of the senior players in the team to take care of the managerial and coaching sections of the club. If he then performs well, the he might be appointed the manager on a permament basis and shall aslo carry on playing for the team.
Some of the recent player-managers in football have been Kenny Daglish of Liverpool and Ruud Gullit of Chelsea.