The problem with a “textbook foot block” is that the concept doesn’t exist. There’s nothing in the rule book that differentiates between a defender’s studs connecting with the ball at the point of it being kicked and a goal keeper stretching his foot at a ball ten yards from where a forward shot.
So, as with everything else with the undefined rules, the refs have to use common sense. For me, if a guys’ studs are in the ground and/or he doesn’t make contact with the ball at the same time as the kicker, it doesn’t make sense.
Otherwise, if a defender is running along tracking a forward and the forward drops the ball and kicks it off the defender’s foot, is that a foot block?