The "F" represents "an offence punishable by a free kick or a penalty kick". It isn't necessarily a foul. But you make an interesting point. Is the substitute really "denying an obvious goal-scoring opportunity to an opponent moving towards the player’s goal by an offence punishable by a free kick or a penalty kick"? Or is he just committing a more general offense of unsporting behavior that should not be treated as a DOGSO-F? FIFA says it is DOGSO-F. Unfortunately, Jim Allen doesn't speak for FIFA (unless he is actually quoting FIFA).
Come on PV. You can't have your cake and eat it too. I ask you for a FIFA source above and you quote me chapter and verse from an outdated ATR published by USSF. And now you tell me that Jim Allen doesn't speak for FIFA? Please.
OK I'll give you the Q&A piece, but I still wonder why you think that an outdated document is a good reference point. Why not quote the most recent Q&A? MK