A pair of scissors, a £300 football boot and one of the stranger-looking kit tweaks in elite football. Pedro Neto had the back of his boot cut open during Portugal’s last-16 defeat against Spain — but it’s not a dressing-room prank.The image of Neto’s sock showing through the heel of his boot prompted the question: why do some players take a blade to footwear designed down to the millimetre?Philippe Coutinho, Roberto Firmino, Mats Hummels and Daniele De Rossi have all worn similar cut-out boots. There could be several reasons for this, but one possible explanation is Haglund’s deformity, a heel condition that can make tight footwear difficult to tolerate.But what is it? How does it affect athletes? And is there a cure?What is Haglund’s deformity?Haglund’s deformity is a bony enlargement at the back of the heel, close to where the Achilles tendon attaches.Michael Robson, a specialist musculoskeletal physiotherapist at LDN Physio, says some people can have the extra bony prominence without experiencing any symptoms.“It really only becomes a painful syndrome when that enlarged bone repeatedly irritates the soft tissue around it,” Robson tells The Athletic.That soft tissue can include the Achilles and the retrocalcaneal bursa — a small fluid-filled sac near the back of the heel that helps cushion the area.Bartholomew Hudson-Gill, a physiotherapist at Opus Biological near Harley Street, London, who has worked with elite footballers at a FIFA Medical Centre of Excellence, describes Haglund’s as a combination of the shape of the heel bone, thickening of the Achilles tendon and irritation of the bursa.“That bursa, essentially, is like a shock absorber,” Hudson-Gill says. “The tendon becomes thicker, the bursa gets irritated, then the bone starts to get irritated.“They load it more, it gets more sore. That soreness means there are changes in the bone, which means it then gets more sore.”Why cut a hole in a boot?Neto has not publicly said why his boot was modified, and a blister or another form of irritation could also explain a cut-out boot.But if a player is managing Haglund’s deformity, opening up the back of the boot can reduce pressure on the heel.