"Porto were quite entitled to take the free kick quickly.....that is beyond doubt."

NO, TUG, IT ISN'T =====


From laws of Soccer ···

Free Kick Inside the Penalty Area --
all opponents are at least 9.15 m (10 yds) from the ball until it is in play, unless they are on their own goal line between the goalposts
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This surely works both ways: not only must defenders retreat 10 yds or to their own goal line; but the kick can not be taken till they have. This law seems quite clear to me.