South Korea head coach Hong Myung-bo has one question to settle in the six-day gap after Czechia. He can trust the back three he built around Kim Min-jae against Mexico, or revert to the back four his players play every week at their clubs.

Hong told reporters that one fixed plan carries risk at a World Cup. “Relying on a single tactic was difficult,” he said, so South Korea had “consistently practised the back-three system” and could use the six-day rest after Czechia to analyse the next opponent and “respond with a different formation.” ¹

South Korea play Czechia on June 11th, Mexico on June 18th, and South Africa on June 24th. The six days in the middle are Hong’s only real window to scout Mexico and change shape on the training pitch rather than mid-match. ²

The shape Hong has built is a back three with attacking wing-backs and two players just behind the striker, anchored by Kim Min-jae. He moved to it only after qualifying. South Korea went unbeaten in AFC qualifying behind a back four, scoring 40 goals and conceding eight, then switched to the back three for warm-up wins over Trinidad & Tobago and El Salvador and named six centre-back-capable players in the squad. ¹

After a June 2025 win over Kuwait, Hong addressed the back three. “It was a short time, but we prepared it,” he said. “It can change depending on the squad make-up, but I can tell you this is part of the plan we are preparing for the future.” ³ By a September 2025 squad announcement he still would not fix it as first choice. “It is too early to decide right now which system, the back three or the back four, is Plan A,” he said. “We used a back four in the final qualifiers, so right now we are at the stage of testing how much the back three can do against stronger teams.” ⁴

Korea’s wing-backs push high in the back three, and the space they vacate has been opened by cutbacks and balls into the channel behind them. Austria scored through that lane when the defensive shape let the ball reach Marcel Sabitzer from an angle that should have been closed, and the same back three conceded four against Côte d’Ivoire. RotoWire argued Hong would be safer reverting to a back four, which sits more compactly and is the shape most of his players use at their clubs. ⁵

STARNEWS reported overseas analysts urging Hong to switch to a back four before the tournament, singling out his three-back tactic as the weak link. ⁶

Javier Aguirre’s Mexico attack straight into the space behind a high wing-back. They press aggressively and break in fast transitions, carry pace wide through Roberto Alvarado and direct forwards who run at a retreating line, and push their full-backs up to overload the flanks. Korea’s back three has conceded from exactly those moves, whether a counter that finds the high wing-back or a cutback from a full-back who has reached the byline. ⁷

Hong can start the back three he has drilled all spring, against the side best equipped to expose it. Or he can revert to the back four his players line up in every week at their clubs, giving up the switching option he spent the pre-tournament building.

Against Germany at EURO 2020, Gareth Southgate’s England moved to a back three for a single knockout tie after a year lined up with a back four, to match Germany’s wing-backs and press man-for-man. England had trialled the back three the previous autumn, so the players could slot into it within a week. ⁸

Lionel Scaloni’s Argentina went further and won in 2022 while changing shape from round to round, with a back five to handle the Netherlands’ wing-backs, a tighter midfield to crowd Croatia, and a left-sided setup that gave Ángel Di María his matchup in the final. ⁹

Mixu Paatelainen, a UEFA technical observer at EURO 2020, said coaches need real sessions to install a formation and asked whether the players already use it at their clubs, the same question hanging over a Korea squad that mostly defends in a back four week to week. ¹⁰

Hong has drilled both shapes; the sources do not show how often other 2026 teams plan to switch. In the six days after Czechia he makes the call. He starts the back three against the opponent most able to break it, or falls back on the back four his players know best.