This is one of the most confusing terms in betting, but one which must be understood in order to avoid disappointment when making multiples bets. The key principle behind related contingency is that you are not allowed to make bets where one result directly effects the price of the other. In cases where they do, the bookmaker can void the bet. Here is a simple example.
Double Check Your Doubles!
Say you want to make a simple multiple on Federer to not only win the semi final at Wimbledon, but also the final. Here the bet becomes a related contingency, as the result from the first bet directly changes the price of the next – if Federer wins the semi final, his price to win the whole tournament will clearly change, and this makes it a bet that most bookmakers will not allow to be made.
Related contingency is confused further by the fact that quite what is defined as one and what is not tends to change depending on the exact bookmaker involved, so make sure that you read the terms and conditions carefully, and if you have any doubts make sure you contact support before making any large bet.