Zonker:
And for your post Sanyarin, another rule is, and I don't remember if you wrote it, but a player can only be under contract with two clubs in each calendar year.
No I did not. That is another thing I forgot to mention

! Thanks (and HOWL) for adding that. But since this rule does not affect the contractual status of a player, but only his ability to play, it did not come to my mind when
CW asked about contracts...
And to give
College Wolf the complete package: Actually things are a little bit more complicated, but I will try to make it simple and just use a few bullte points...
1. A player can be UNDER CONTRACT with as many teams he likes during the period from July 1st to June 30th of the subsequent year.
2. He may be REGISTERED as a player only with three teams during that period (registration is required for a player to be allowed to play for the team).
3. He may PLAY IN OFFICIAL MATCHES (thereby excluding exibition games) only for two teams during that period.
That means he is unlikely to switch teams more often than two time per years since the new team would not be able to make big usage of tha player, but legally, he can change teams as often as he wants.
EDIT: Those regulations are often beneficial to teams which want to buy a young talent with lots of upside, but do not see a chance that he might crack the rotation sometime soon (maybe because they are in the title hunt and can't afford to give playing time to unproven youngsters). In that case, they can buy the player from the team he was registered with, but refrain from registering him themselves, leaving one unrestricted registration \"open\" for another team, enabling them to loan that player to a small market team where he can play one or two full seasons to gain experience and develop.