semeai

The fact that people play the Ace here too often seems related to economics studies showing that people will avoid a loss more than they will seek out an (e.g. equal) gain. That is, the Ace is obviously my right as a trick, so I don't want to lose it, even if by risking it (even if it's fairly low risk) I will often gain (a less-obviously-mine trick later on).

I know nothing of ABF rules, but presumably one hand is not enough to conclude there's an agreement. Did they admit they regularly opened this sort of hand or was there some egregious fielding of this psyche?

Definitely A. B would lose the spade suit. Once you're game forcing, bid 2♦, though some choose to bid 1♠ first even then (a substantial minority have this treatment, I believe). When you're strong enough to bid 2♦, but not game forcing, it's more of a tossup. Perhaps most still bid 2♦ in this situation.

I didn't at all mean that a good player wouldn't underlead. Just that it wouldn't be automatic for a good player because there is some risk.

Thanks, glad to be here!

Who knows, but I'll be normal and play the 10. Four reasons: 1) RHO is more likely to bid 2C on Kxxx than Jxxx. 2) If RHO has Jxxx, I'd say it's more likely that comes with the heart King. He won't have the spade King, else he'd discourage I'd think. I think he'd just pass with QJx-xxx-Jxx-Jxxx or worse as he really doesn't care about the suit. 3) An Ace lead from AJx in the suit partner bid is reasonably likely given any hand I construct for LHO excluding those with KQJ of spades. 4) It takes something extra to play someone to have underlead (and there is risk to the underlead so it's not as though any decent player will do it: maybe I have two clubs and two spades and he needs to set up the spade trick now). Of course, I still could be wrong.