$350 live - Open ender plus two overs.

I would be more than happy to gii on the flop as described because heads up, villain is almost pot committed, and can't get knocked out.

So, maybe if I think villain is decent player, I would wait until the turn in case we improve or the board pairs the deuce and I get to see what he does on turn.

I am generally amazed by the number of times someone will stab on the flop and check the turn/river.

If he open raises and has done a few 3-bets I don't really understand why you still label him as loose passive.

The only thing that seems sure is that we're behind atm. No matter what might be a correct description of villain I don't see him doing this with high Ax-hand including A9 into 4 other players. Even 77/66/55 seems unlikely. If you think he's on the passive side he could very well have called with QQ/JJ. But the most likely hand seems to be 99, 88 or 98. Perhaps 22, although this seems a bad call here pre.

Either way I don't think we can count on a jack or a ten as outs for Hero. Which means straight + backdoor flushes are the only real outs. And because QQ might be in his range some of our outs are blocked.

Under such circumstances you don't have the right odds to call. You are also OOP, making this hand more difficult to play. His SPR also makes it likely he'll shove most turns when you check, forcing you to fold every time. To make this passive line justified I think you have to make an assumption that a lot of his range is A9 and JJ/TT (which you obv block) and that you'll be able to blast him of such hands OTT on most cards (not only an A or a K).

CR the flop all in seems a bit better, but still I don't think Hero has much FE here. Especially if he really think Villain is loose passive (which makes a wider range including semi- or pure bluffs even more unlikely). I have problems myself folding good draws in spots when they probably aren't profitable. But I believe this might be such a situation, justifying a fold albeit it definately is on the real tight side.

I think villain can have 9x. Even 8x without 2 pair or a set. If I were in Villain's spot I would absolutely bet 7k with a single pair here because if the turn is above a 9 it means we will have lost control of the hand and in all likelihood be behind given there are 4 other people in the hand.

So I would c/r jam. I did it yesterday in a WSOP main $1200 satellite at Foxwoods when I raised UTG with T9s and the flop was 762 and I had a flush draw. I checked because there were 4 players and the BTN bet and I c/r jammed which would have put him all in like this situation. He tanked and decided I had an overpair which would have been a good way to play an overpair.

Here we only have a BDFD so we may not have as many outs but I think its worth taking a shot at it.

Preflop
Standard open.

Flop
I can get onboard with a check here. However if they are going to call far more often than raise, there is also an argument to bet on the small side to kind of set your own price to draw. I dont think, there is much chance, that a single bet get all 3 players to fold. As played its 100% a check-jam against a short stacked opponent. He is not likely to fold very often, but by getting it in now, you are sure to get his stack, when you draw out on him, and you dont risk facing a turn jam, which you cant call.