During his time in Shield, he was diagnosed as having a form of Autism which goes a way to explain his superior accuracy, not to mention his ability to pick up new skills quickly, such as martial arts, hacking, lip reading and becoming fluent in other languages, not to mention his loner reputation and his focus on his professional life as opposed to his social life outside of Shield. On the outside, Clint looked and was treated like any other Shield Agent as he did well to hide his condition and only really became an issue with social interactions which Clint did his best to avoid if at all possible but managed to get through them if he had to.
Normally being diagnosed with a form of Autism would mean he wouldn't be suitable for military service, however, Fury told the doctors that he would use his personal discretion and used his clearance as Director of Shield to keep Clint in the Field as an Agent and even went as far to have it omitted from Clint's Shield personnel file. Clint would also be diagnosed as suffering from Generalized Anxiety Disorder as well as severe depression.
During Clint's time at Shield, he fell for fellow Shield Agent Bobbi Morse and the two start a relationship and eventually got married. However, due to their professional commitments the pair eventually got an amicable divorce.
Also during his time as a Shield Agent, Fury sent Barton after a Russian KGB officer called Natalia Alianovna Romanoff who had been making her name for herself as the codename Black Widow due to her ruthless effectiveness. Fury issued the order for Clint to eliminate Romanoff due to both her expertise and her growing threat to global security. However, upon observing Romanoff he refused to carry out the orders instead managed to convince her to come back to the States with him and become a member of Shield much to Fury's annoyance. Clint was ordered to observe and supervise her training and evaluation during which the two became close and would go on to form one of Shield most highly regarded partnerships with the designation being Strike Force Delta. Many people who worked alongside Clint and Natasha (as she chose to be called) commented on how the two of them were closer than any romantic couple or even any longtime married couple. However, the two of them kept things professional due to their work commitments and neither wanting to ruin their extremely close friendship not to mention partnership.
It was also during his time with Shield that Barton was sent to New Mexico by Fury to investigate a 0-8-4 and after a while at the site, an intruder would break into the site and Barton couldn't decide between his bow and his trusted M40A5 customised sniper rifle, so he grabbed both and would use his M40A5 sniper rifle if he was given the kill order on the target.
In his downtime from Shield he would train a protege in Kate Bishop as well as adopt a dog in the form of Lucky, a Golden Retriever who saved his life when he was confronted by a group of local thugs, Lucky was badly injury as a result and Clint rushed him to the nearest vet