England’s football team is treating their World Cup game plan like a private key: share it with no one, guard it with everything. The squad has delayed its departure to Mexico City for their Round of 16 clash against Mexico, choosing instead to hunker down at their secure base camp in Kansas City over concerns that rival eyes might be watching their training sessions.

Manager Thomas Tuchel wants his team to finalize tactical preparations in a controlled environment, free from the risk of observation. England’s Football Association decided that an extra day or two of privacy in Missouri outweighs the benefits of early acclimatization to Mexico City’s altitude.

The tactical calculus

England’s base at Swope Soccer Village in Kansas City sits at roughly 250 meters above sea level. Estadio Azteca in Mexico City, where they’ll face the hosts, perches at approximately 2,200 meters. That’s a nearly 2,000-meter altitude gap, which normally would argue for arriving early to let players adjust to thinner air.

The fact that Tuchel and his staff chose information security over altitude preparation tells you exactly how seriously they view the espionage risk. In English: they’d rather be slightly out of breath than have Mexico know their set-piece routines.