I thought about this.
So we all know that sometimes it happens that the only player in the blue team gives lr, and then next round switches to the red team so that the freedays get lost, and then he joins again once the freedays are gone. It surely isn't plesant to see this happen if you are the one who's losing the freeday, but I don't know if banning instantly the blue player that goes away from the blue team would work.
I wouldn't like to think that I could be banned just for leaving the server/the BLU team at the end of the round. Someone may just need to leave the server for real life obbligations or be tired to be in the blues, and I wouldn't want to see him banned from guards just for that.
Also, what happens if a warden is very good and keeps delivering lr every round? Does he need to stay on the BLU team forever? In that case he would need to get killed or not give lr on porpouse, in order to not get banned. What happens if, for example, the parents of a BLU player enter in his room and he can't talk anymore? Do we ban him for that?
The ban would also be very avoidable. Even if we would ban a blue for waisting lr in this way, he could just waste the freedays by getting himself killed on purpose (e.g. falling accidentaly into sweeper).
But if we do want to create a rule like this, then I tought we could do something like this:
If someone is blue, he is the only one, he gives a lr, and then he switches to the red team to waste the lr, we could create a rule like this:
"If there's only one player on the BLU team and he gives lr to a player in the RED team, the BLU player is allowed to leave the BLU Team/server in the next round and he won't be punished for waisting the lr, but if he does that, he is not allowed to join the BLU team for the next 3/6 rounds (the time should be discussed, we could also set a time in minutes (30/40 minutes)). If a BLU player wastes the lr by leaving the team and then comes back before he is allowed to, then such player will be guardbanned."
A rule like this would not harm the BLU players who genuinely need to leave the server/blue team, and it would encourage the other BLU players to not waste the lr.