Quote from dont:
My question is, what are these guys trading off? A model of how the equity and debt should behave because if thats what they are up to I am not surprised they are seeing their arses.
No, that's not it - it's coming from CDO world "equity vs senior", not stocks vs bonds. A number of hedge funds engaged in what is known as "correlation trading". The structures that provide for this kind of trading the best are CDO (Collateralized Debt Obligations). CDOs in a sense are baskets of low-grade bonds. The pay from these bonds is split into tranches, tranches are paying in what's called "waterfall" structure. In short, senior tranches pay always and are rated AAA. So, if something defaults, they still pay their coupon. Mezzanine tranches are the first to recieve everything that's left after senior tranches. On the very bottom, there are "equity" tranches, which are piles of shit paying very high coupon.
So, given this structure, you can find "arb" in form of payment/probability mismatch. Let's say mezz tranche paying 5% with 5% default probability for every bond, while equity tranche is paying 25% with 15% default probability for every bond. It's only natural to say - well, let me buy 1 unit of equity tranche and sell 3 units of mezzanine tranche to be hedged against default. Nice carry of 25 - 5 * 3 = 10%. Free money, right? The only problem is that if a bunch of companies decide to default at the same time, your equity tranche will suffer much more. In a sense, you are buying implied correlation vs historical correlation.
That's exactly what happend in the past few months (automakers all correlated) and since the tranche purchase are financed on margin (well, repoed out, which is the same thing), some positions had to be unwound. Some big positions, to be specific. That's what we see.