DP / Flex and CR

[DaveASA/FED]

Ok, I will probably get hammered for this but here goes. 1st (simplified for my weak mind) in the top of the first inning only person labeled at F1 and F2 can have a CR, in bottom of 1st and all other innings whoever last person was that held the F1 and F2 position when the 3rd out was recorded can have a CR.

2nd I agree that the situation used above with the coach batting the DP then subbing the Flex (F1) for the DP and then trying to get a CR is unethical but is it illegal? I mean what rule specifically supports it not being allowed? You can subsitute the the Flex for the DP right? And you can have a CR for the person who last played F1 right? So I agree it is sleezy but what is the basis for asying it is not allowed by rule?

Not trying to start a fight just trying to understand. Also I agree that this could only happen twice with the original DP as that player would be out for the rest of the game, coach could sub another player for the original DP and keep going till he ran out of players.