Now, I know today that libero refers to a sweeper and I identify the position with German great Franz Beckenbauer. Back in the day I thought of the libero as more of the stopper or holding midfielder in the 4-3-3 tasked with disrupting the opponents attack and rhythm of play. The advent of the modern offside rule has seen man marking systems give way to zonal defending and hybrid systems. The sweeper position of Beckenbauer's era is all but gone with the role of the libero shifting to the defensive or holding midfielder.
In today's game the backs in zonal systems share the workload of Beckenbauer's libero in covering deep for one another. It actually is the holding mid or defensive mid that is tasked with a proactive sweeping of opposition breakthroughs as they patrol in front of center backs "protecting" against the generation of through balls on the ground or in the air as well as against long shots being taken. In this sense they are free or libero.
In bringing together players from multiple high schools and differing systems one challenge I face is in defining positions in a manner all can understand. Understandably every coach and system have their own terminology. I suppose I compound the problem even as I attempt to simplify things for the players on my club team. For our purposes the holding midfielder is designated as position #6 and tasked as follows: