Online 30/60.

Normal reg (on the looser side ) opens OTB,
LAG (44/25, not horrible, but somewhat erratic, too aggressive in various spots, for example 3bets postflop too much) calls in SB.
Hero calls KT in BB.

Flop (6sb) AQ5

LAG and Hero check, reg (BU) C-bets, LAG (SB) raises, Hero…

Since LAG called pf, is somewhat erratic and aggressive, he should have fewer aces in his range when he x/r's than otherwise would be expected. It's not easy to count the outs here, with the weak bdfd and super weak (but still non zero) pair outs, with a mixture of implied and reverse implied odds. I'm currently getting 4.5 to 1, but the pot of course could grow quite a bit by the river. During the game I felt that all three options were worthy of consideration, which made this hand memorable.

Fold and not close.

Not close

Right. There are two of them. Sb may indeed be check raising light. But you're parlaying your hand against his range AND button's. Bad things can happen when action gets back to button. You almost never have the best hand. You don't have the odds to continue here.

Flop is easy fold. More interesting decision is whether to 3b PF against their loose ranges.

Don't 3b pf (IMO). I'd rather play KTo for 6sb in good relative position to both the pfr and a lag (action can very welcomingly be k,k,b,kr; b,?; or k,k,b,c giving me the kr option or call) than bloat the pot to 9bets and be stuck with off suit paint where I'll be the one acting first on virtually every flop. Even if it has an equity edge, that calc doesn't really show playability on later streets and the edge will very likely be small (so we'd not be giving up much if anything).

And in a surprising throwback concept (HPFAP....wow haven't typed those letters in nearly forever), don't bloat the pot in a blind battle making opponents play correctly by calling "too loose".

You're right though that the pf decision is absolutely the most interesting part of the op.

What do you mean by that? If you want the pot to grow then you can always 3bet.

Lag has ****, button opens wide. There's actuLly nothing wrong with 3 bettin this pf. If it was suited I'd 3b more than I called

By that I meant that currently the pot is way too small to justify a 1BB investment by itself, no matter how you count the outs, but by the river it would grow so it's less clear. 3-betting would defeat the purpose of course, because now the investment is larger. In other words, all I was really referring to was the fact that we have good implied odds on 4 of our outs.

I won't claim that folding is incorrect here, but I do think the situation is less clear-cut than would appear from the responses so far. I think the answer really depends on the range that we assign the SB. In particular, if he almost never calls preflop with Ax, which is probably true for many players, then in addition to our 4 gutshot outs and weak bdfd, we would also have decent pair outs to a king (and pretty weak but still non zero to a ten), and even weak showdown value. In that case, it would be unreasonable to fold.

In reality, we should not be assigning such a lopsided range to SB, given the limited information we have, but it's still conceivable that on average a player with this description has an insufficient number of aces in his range to make folding here "not close".

You are ignoring BTN's range.

Say BTN opens 50% = ~660 combos. BTN will have ~150 Ax+ combos, ~90 Qx combos.

23% of the time, you draw to 4 outs and likely to get sandwiched.
14% of the time, you draw to at best 7 outs.

Now factor in SB's raising range and discount your outs even further.

I was certainly considering BTN's range in what I wrote above, though I can see that it wasn't immediately apparent since I never explicitly mentioned BTN. But if BTN wasn't a concern, I don't think folding would even be an option, there would be nothing to discuss in my mind.

The point of my previous post was that if we knew that SB has almost no aces in his range I think it would be unreasonable to fold. If you agree with that hypothetical then there's not much disagreement here. If you don't agree, then I would be curious to understand why. It's true that in the 37% or so cases we are drawing to 4 or 7 outs against BTN (though I have to mention that he opens more than 50%, he's a reg, but on the looser side), but that fact doesn't make it in any way obvious that we should be folding.

What? Certifiedly folding is an option even if you're ignoring btn. You're going to have 7 outs to a Q a lot of the time in 4.5 BB pot.

What range are you putting SB on? If you continue if this hand you're basically praying SB has middling diamonds and you already have the best hand

fold