Manchester City locked in a $100 million player for $5 million, and they did it three years before the market could bid. Here's the mechanism. FIFA bans international transfers of players under 18. So when every big club in Europe wanted 14-year-old Cavan Sullivan in 2024, none of them could actually sign him. City found the workaround. They negotiated a clause inside his Philadelphia Union homegrown contract that transfers him to Manchester automatically when he turns 18 in 2027, for a fee of…