This hand comes from the Geelong Congress Teams event. South opened 1S and, after the double, North jumped to game. This is correct since there is a 10 card trump fit and the Law of Total Tricks suggests bidding for 10 tricks and North has 7 losers ( only one in spades because of the 10 card fit) and 7 losers opposite an opener is sufficient for game. Even those who rely on point count should add 3 for the singleton and reach 13 and should bid game. If NS were playing a natural system where South might be strong a 4C splinter bid would be the best choice. However, NS were playing precision and, since South was limited to a maximum of 15 hcp, there is little chance of a slam and the leap to 4S was clear. East reasonably bid 5C and North decided to bid one more and that ended the auction. If the vulnerability had been the other way around, East might have bid 6C as sacrifice but this is rarely a good idea at adverse vulnerability.
Since they have both shown clubs ( double promised the other three suits), West led the obvious QC and East won the ace. East continued a heart to the queen and ace and declarer had to find eleven tricks. The bidding has been quite revealing since West doubled and East has shown the AC. This means that both diamond honours are offside. There are also plenty of trumps so an elimination play looks best. The next question is who can have three trumps. The take out doubler is short in spades so only East can have three so play the AS first and then a small one to South for two more rounds. Cash the KH, cross to dummy with a trump, cash the heart jack and then play a diamond to the jack. West will win this but has to lead a diamond away from the other honour or give a ruff and discard. Surprisingly, 25 of 34 tables played 4S. Perhaps West, weakly, did not double 1S because East would surely bid 5C after a double. EW are unlucky that it is difficult to find the killing diamond lead after the 5C bid.