Popularised by Guardiola, the inverted full-back tucks inside to become a third midfielder, turning the team into a 3-2-5 in possession.
This move gives the side an extra body in build-up, frees the inverted wingers to stay high and wide and provides rest defence against the counter.
Not every full-back can do it: the role needs composure on tight touches, awareness of diagonal passing lanes and the ability to press centrally without losing balance.