Originally Posted by BullMcGiveny
^ He gives the not personal line before attacking Cap, so I don't think that is it.
I don't think Brock turns so much as he reveals his true colors.
He probably starts out as kind of a competent agent who Steve could be bros with, but when someone gives the orders, he has no qualms about turning on him.
Rumlow is probably a bad guy from the start; he's just another HYDRA mole (and there are plenty) pretending to be a loyal SHIELD agent.
THE COTTON AVENGERS
...They move like slick cotton on oil.