Because of the route than was ran. And how the play played out. You can pretty much use process of elimination. Also there's a quote in the Chronicle where Jason Allen and Vance Joseph were talking about how they were expecting and preparing for the back shoulder fade, and he benefited from his work in practice. But its pretty clear of what Gabbert was trying to do even without seeing those quotes. It just looked like it was poorly executed.
What other route did you think it could be? The only other routes it possibly could be is a deep curl or comeback, but it would have still been a poorly thrown ball.
I agree; the only attempt a QB can make here is a back shoulder fade.
With safety over the top and the CB running with the receiver (instead of playing underneath at the start), the QB cannot risk a throw over the top for fear of the safety.
A pass to the inside (unitended in this case) is there for the CB to play when he knows he has help over the top.
The only attempt a QB can make is going to the outside on a back shoulder fade.
As is, it was a terrible throw by Gabbert.
He shouldn't even make the throw in the first place.
If you rewatch the play, the Jags had two receiving threats on their left (Allen's side) and thee on the other side.
The Texans rushed four (evenly with two rushers on each side.)
We dropped four (Allen, Nolan, Quin, and Cushing) on Allen's side to defend two (MSW and MJD) (even though Cushing can also help on the TE .)
We dropped only three to defend three on the other side.
This is an example of what I've been saying.
The Texans roll help over to Allen's side quite a bit more (baby-sitting).
With Joseph and Jackson, they were treated more or less evenly, there was no discernible trend with those two in coverage.