WGTChampion: To the best of my knowledge it has always been that a player needs to leave their club before trying to join another.
That is correct. But, owners and others with admitting privileges could invite players who were a member of another club. That is really important to me right now since we are trying to do a merger with another club with the cooperation and help of their owner. Obviously, accepting that invite got one kicked of first club.
It also meant that a player who was looking for another club could ask for an invitation without quiting the club he was in.
(I completely agree with remarks above about not raiding another club, and I have complained about specific people in the past who were doing it.)