A guy I was playing with routinely doubled the blind preflop whenever the action was limped to him and he was the BB. I haven't played a lot of poker and am trying to understand what he was doing. There were multiple players in the pot so the raise was not big enough to drive anyone out. Pocket pairs are weak against multiplayers so I can only assume he had AK or similar. But AK will only hit 30% of the time, probably less against multiple players. I understand doubling the bet if you have a made hand and are betting for value, but we were going to see 5 more cards and there were 4+ people in the pot.

Shouldn't he either check or make a big bet to try to scoop up the limpers?

Lol no doubling the blind is not a good play. It's particularly bad when facing limpers.

It isn't that min-raising one's own big blind is a bad play -- given any particular formation of limpers, I am sure that there is a range for which min-raising is (a) profitable and (b) more profitable than closing the action with a check.

Here are some good things that can happen when the big blind min-raises limpers:

• It gets money into the pot when the BB has a high-equity hand that plays well multiway.
• It halves the SPR, reducing the disadvantage of playing the rest of the hand out of position.
• It can increase the limpers' emotional investment in the pot, making them stickier postflop if they make marginal hands.

The issue is that at typical cash game stack depths, min-raising limpers from the big blind is a dominated strategy: there exist strategies that outperform it, such as raising substantially more (e.g. to 4bb + 1bb for each limper in a cash game with 100bb effective stacks) with a tight, linear range and closing the action with a check with everything else.

Good point, and in general we should be careful to not confuse +EV play with optimal play. If you are dealt AA, for example, it would be pretty hard to come up with any strategy (well, maybe fold preflop) that isn’t +EV. That does not mean that any way you play AA is optimal.