On this deal from the 2015 NABC Senior Knockout Teams (in Denver), Bart Bramley had a chance to make 4XX:

Vul:West Dir: N-S	Q10986  8  AQ  Q10953
3  --  J10987653  A642		AK7542  K752  --  K87
	J  AQJ109643  K42  J

West opened 4, passed around to South (Bramley). He bid 4 and when this came to East, he doubled for penalty. North redoubled (not clear how he meant it), but there they rested. A diamond was lead and East ruffed. He laid down a high spade, all following. East now (reasonably) played a low spade. He didn't realize his partner had no trumps. Had Bramley discarded his club, he would have made 4!HXX for a whopping 1080! However, he didn't know the strange position. He trumped with the HQ, played the A and a high heart to East's king. Now a club to the ace enabled another defensive diamond ruff for down 2, -1000. Big swing? Yes, but not how you would expect.

This was the auction at the other table:

West	North	East	South
Rodwell		Meckstroth
5	Pass	Pass	5
Pass	Pass	Double	Pass
Pass	5!	Double	All Pass

Yes, Meckstroth got to defend against 5SX. The play was bloody and ended up with a penalty of 1700 (down 6). So, Bramley won 12 imps for going down 1,000!