Deputy involved shooting at Inova Fairfax Hospital.

This is interesting.

Video of a deputy involved shooting at a Fairfax, VA Hospital.

This incident occured on August 15, 2016 at Inova Fairfax Hospital.  At about 50 seconds in, you see Mr. Gomez start swinging at the security officer.  At 3:20, the deputy arrives on scene.  At 3:30, Mr. Gomez charges at the deputy.  At 3:34, Mr. Gomez falls to the ground.

For the most part, private security ony observes and reports.  When the guy started swinging at them, they did as they should and they got out of the way.

In Fairfax, there is both a Police Department and a Sheriff's Office.  Now the deputies tend to handle the courts and civil matters, while the police are tasked with the handling of legal matters.

I'm not too clear on why the deputy was at the hospital.

There wasn't much time for the deputy to defend himself.  If I recall correctly, deputies in Fairfax are not issued Tasers.  On an aside, the 9th Circuit ruled that Tasers were tantamount to lethal force, so many agencies are now getting rid of them.  (My agency is letting the majority of them age out, while most of our officers are not even bothering to carry them.)