When this happens, a mass pickering sets in as an automatic consequence (though, as mentioned, no one realised this when Crescent '31 was drawn up). All stations inside the Circle Line are mapped to locations outside it, and vice versa. This has a very destabilising effect on the game, since far-flung token stacks in the outer zones are brought close together, with unpredictable results, and Beck's coefficient tends asymptotically to infinity. In the 1970's Trellis National League Long Game, a Circle Line Inversion lasted so long that real versions of foetal ghost stations quantum tunnelled in from parallel universes, and there was no play for the whole of 1976 while an extremely hazardous exorcism was carried out by a special team from the Vatican.
The first player to recognise that such an event could occur was the great Hugo, who famously used it to gain victory in the final of the World Championships in 1935. Ruttsborough, in the audience for that amazing game, immediately began using this tactic in games against opponents who had not yet heard of it and its provenance was, for a time, falsely attributed to him; a mistake he made no attempt to rectify in his 1937 classic "Invert This, You Piccadilly Piccanilly!"
Debates raged for many years over whether the Circle Line Inversion was a dazzlingly bold manouevre that should be celebrated or a hideous anomaly that the rules should be altered to avoid. These went unresolved throughout the '40s, with the various rulesets drawn up at that time alternating between one and the other ([Praed Street '41]? in particular is notable for its drastic policy of putting all termini in permanent spoon to prevent such an occurrence). After various incidents of chair throwing at meetings by Ruttsborough supporters, Circle Line Inversions eventually became a permanent feature of the game starting with [Marble Arch '54]?.
The only safe place to be during a Circle Line Inversion is at a non-interchange Circle Line station. The effect can be reversed by a circuit of the Circle Line in the opposite sense to that which caused the inversion in the first place. In general, all players cooperate in such an effort, though the more aggressive may welcome the chaos unleashed.