This thread is years old but in case anyone reads this I just want to inform.
I am a Chess tournament leader.
There has never been a rule about perpetual check in chess.
It is not needed.
As, there is a rule of repetition:
If a player can make a move so the same position would come
- for the third time,
- with the same responses being possible[*]
he can claim a draw if he announces it in advance - not _after_ making the move.
[*] Despite the positions being 'identical', the responses being possible may not always be the same.
E.g. if there is a black pawn on b4 and white plays a2-a4 the position would not count as the first of three.
Because, Black could in this position play -,b4xa3 'en passant' - but this only possible right away not later.
Similarly, if White could castle but decides to play Ke1-f2 and then Kf2-e1, the positions is not "repeated", as White can no longer castle.
Perpetual check is a standard way of drawing on all levels of tournament chess.
It is not for a split second being regarded as unsportmanslike by any tournament player.
Here is a collection of master chess games where the defending part finds a clever way to draw by perpetual check.
www.chessgames.com/perl/chesscollection?cid=1005586You will not find a single comment from anyone talking about 'unsportsmanslike conduct'.
* In chess a perpetual check is simply a completely legitimate way to draw *
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In contrast, the check-receiving player would be regarded as unsportsmanlike if it was totally obvious that the checker could go on and would have to, but it would take some time before a certain position was reached for a third time.
Wasting his opponents time this way would be senseless.
This is a rare occasion, and it is usually totally OK to defend against the checks until the opponent claims a draw by repetition.
In most positions it will be obvious that a person can go on checking, and the checker would offer a draw on that basis.
Again, refusing this draw would be senseless.
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In correctly working chess-playing software there is an option for "Claim draw by repetition". By clicking it, the software will close the game as drawn, otherwise respond "Claim invalid" and let the game continue.
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Finally, there are lots of situations in chess where there are no better option to repeat moves, as everything else would lose, checks or not.
Nobody is obliged to stop this for his disadvantage.
In the early days of chess there were no rules about draw by repetition, and so the players might go on for a couple of moves more, to test if the other party would take the risk of breaking out of the sequence.
There is, to my knowledge, a single historical example where any of the players would go on repeating moves, instead of just agreeing to the draw.
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So happy perpetual checking - if you don't see anything better!
And if you otherwise have the advantage - look out for your opponent stealing your win away.
