The John Barnes is a tactical approach to team games or strategic board/computer games. It refers to an attempt by the aggressor to outflank or attack their opponent to the rear, or to infiltrate their defense.
It refers to John Barnes the English footballer who famously rapped a portion of an official England football song a section of which went as follows.
"They will hit you and hurt you, defend and attack. There's only one way to beat them, get round the back"
When faced with a stout defense from 300 Spartans, the Persian king ordered his troops to John Barnes the enemy thus encircling them with the use of an alternate path.