Missed When Appropriate, Used When In

J 10 8
7 2
K 9 7 5
A 8 6 3
A 9 4 2
A Q 10 8 6 9 5 4 3
10 4 3 A 8 2
7 2 K Q J 10 5
K Q 7 6 5 3
K J
Q J 6
9 4 Vul: E-W

EastSouthWestNorth
Pass 1 2 2
4 4 Pass Pass
Dbl Pass Pass Redble
All pass

There were 8 missed redoubles in heart games -- five in 4 hearts, three in 5 -- and one inappropriate redouble in 4 spades. Well, I shouldn't say the 5 bidders missed a redouble, since you can't make 5 on a diamond opening lead, though no one was getting it in light of the spirited bidding in spades. I have chosen to display the spade redoubler, partly because I feel I'm on a little solider ground with that redouble than with the omitted redoubles and partly because there's not much to convey about the latter. Over 4 hearts, South bids 4 spades. It's an ambiguous bid, to be sure. In the absence of a 4 heart bid, a leap to four spades would show a big hand and of course an expectation to make. Here, it's not clear whether South is bidding to sac or bidding to make. North should let it go on the ground that if bidding to make, the double should guarantee a pretty good result anyway, not to mention the times people have bid to make and gone down for one reason or another, and on the ground that if his partner isn't bidding to make, is bidding to sac (and it's a good one, of course), well, you certainly don't want to double the penalty in your sacrifice bids, do you?
As for the heart bidders, well, it's hard to tell just how confident they were. I went to a couple of the 5-level bidders and didn't see Blackwood, but rather a bid over 4 spades, so it wouldn't be proper to say, Hey, gee, you missed a good bid on a redouble (which I would be inclined to say if they'd tried Blackwood and abandoned slam). Still, one would think the 4 bidders especially would have felt confident enough of their potential to come back with a redouble. To be sure, there's a downside to redoubling even at the four level. What do you do if the opponents now run to four spades? Double them or go to five? And if doubled in five? Redouble? Whatever follows (aside from acceptance of the redouble), it's not good for the heart bidders. So I must admit to not a little ambiguity about the heart bidders, who might well be making the best choice by passing the double. But I feel no ambiguity about the incautious redouble of 4 spades. As said in reference to earlier redoubles, if you make, you've already got a good board, and if not, then obviously the redouble only doubles the penalty. North is looking at two low hearts, a very modest 3-card trump support, on top of which, suppose South is making a sac. Do you want to punish him for it? Four spades doubled figures to be minus 300, which is significantly better than the opponents' vulnerable heart game.