Black Widow is known for being a great spy , athlete and assassin. She was once an enemy of Avenger but joined them when she did get out from U.S.S.R. grasp . She was well-trained at a very young age as KGB's Red Room Academy. She did excel in many ways when it comes to martial arts and weapon handling.She has been the top agent of S.H.I.E.L.D . Source here
image sourceThere are also times that the Black Window serves as a Team Leader when Captain America and the members having a internal ethical disputes on Kree-Shi’ar War. She did great as a team leader since she knows the tactics and strategy which has been her expertise as a spy.Source here