I'm BB at 300/600 with about 35k, I have pocket Jacks and make it 4k to go pre-flop. 2 callers.

Flop is 864, 2 spades. I make it 11k, loose aggressive to my left goes all in with enough to cover me (by about 4k), other player folds, I call all-in, he turns up A4 of spades.

He called off 19 BBs with a Flush Draw, should I have went all-in? or folded when he jammed leaving me with about 20k behind?

Hi mate, is that your standard open sizing, or did you raise larger because you had JJ? Perfect size here is the same as you’d open with any other hand - 1200 to 1500 - towards the higher end if you don’t have many <25bb (shoving) stacks behind. Never raise larger with JJ than you would with other opening hands in the same position.

Postflop you’ve cbet another huge size - but I understand why as you are protecting the overpair on a vulnerable flop. No choice but to call the Jam and good luck on the runout.

We can raise larger pre to exploit / target opponents that play poorly against odd sizing though - so if you did that in response to a particular table dynamic, I’d be interested in the details.

Sounds right to me, including the opening raise questions. I don't mind the larger c-bet on a board like this, where so much can change that's bad for your hand-- the flush, the one-card straight, one of the overcards.

And calling the jam vs. a loose aggressive player is fine; he's almost certainly going to have good equity, but the pot is too big at this point that you'll just have to fade the mostly 12-15 outs (you are behind sometimes, but I think he's always going to get it in here with his good draws). As played, you're calling 20k to win 55k; flipping with those odds is totally fine. Your hands just gotta hold in spots like these to win tournaments.

I may have raised a little larger than normal. This table was very aggressive, most pre-flop raises were 2000 and up. I appreciate the responses, I just kept wondering if I jammed on the flop instead of the 11k, does that get me the pot. Agro on my left may have called anyway, it's one of those hands that kind of haunted me all night after the bust out.

Its important to know who your opponents were (what positions they were in) and if they limped in or raised pre-flop given that you were the BB. If they limped in it is also important to know if they had limped in before (or if it was standard at the table to limp in).

Assuming that they limped in and had done it before, I would have raised to about 3600 but I have no problem with the 4000 which is close.

As played, given that the flop favors the limpers range I would not be betting 11,000 on the flop. I would be betting closer to 33% Pot which would be more like 4,500. The other reason not to do that is that it commits you to the pot on a jam because you are putting in over 33% of your stack (which is the effective stack size given that you are covered). And because it is fairly obvious that you have an overpair when you bet that much, it makes it easier for opponents to play perfectly against you.

If you had bet 4,500 on the flop your opponent still might have jammed but he might have just called hoping to get another call and increase the pot. If he just called your 4,500 flop bet and the turn wasn't a spade or an A, you might have been able to get a fold if you then jammed the turn. But if the turn was a 4 it wouldn't have mattered anyway.

Given the bet sizing on the flop I would have called. You got it in good on a flip that you were slightly ahead with a lot of dead money in the pot.

As to whether jamming the flop is a good idea I think it is better than the sizing you chose but worse than say 4500. Your opponent may have called anyway given you could have AK or a smaller flush draw (like KQs) for your jam. And even if you have a pair he would be flipping with over 12,000 chips already in the pot - so it would be a good call on his part.

ty Rick I see there was some pre action missing in the OP