Credit Rob for getting his head around and catching the ball, but it was poorly thrown, a poorly run route, and the WR (Blackmon) gave up on it and let Rob have the ball. Now, I realize it's practice, but our WR's could use some practice playing defense on poorly thrown balls.
I don't know if he drifted back to the post because that's where the poorly thrown ball was going, but he got separation by cutting to the flag. He was wide open if the ball had been thrown to the flag.