Bucky, unable to tolerate the thought of anyone else wielding Steve’s shield, sets out to steal it while it’s being transported. It’s then that he sees Natasha for the first time ...

The reason why Natasha was trying to throw Bucky off his game also sits well with a scene in the movie when she told Steve Rogers that they met when Bucky killed someone she was protecting.

Sebastian Stan, who plays Bucky Barnes in ... "Do I want Steve back? Steve Rogers should come back," he said. "I think that would be fun. Who else? Natasha, obviously, there’s about 27 films ...