...in that video if you look Blackmon had to turn back and pause momentarily to make the catch. At that point the safety is already in a dead on run and has the angle. I don't get the sense from the way Blackmon is running that he's running all out. He looks to me like he's waiting and hoping to maybe get the guy to overrun him a little so he can cut back on him and use his momentum against him.

The pause and turning back to make the catch happens at the 39 yd line and the safety is only a yard behind that (maybe a touch more). The safety had a good angle and it took a few strides for Blackmon to get back up to speed. By then the safety had pulled even and had the angle on him. Makes sense that Blackmon would see the diminishing real estate between him and the sideline and start thinking about drawing the guy in to use his momentum against him.

Just my two cents worth.