So last night at a sanctioned wizards of the coast event, i witnessed something that I would like to run by the community at large and gather some opinions about. While playing in an event at a LGS a male player walked up behind a female player engaged in a game and leaned all the way until his face was about two inches from hers. A person that knew her said to the male player “I don't think she is going to like that.” The player stayed there. The female player turned and upon seeing the person said “Please get out of my personal space.” The guy stood and said “what?” then leaned back in. She repeated, “Please get out of my personal space.” He stood again just behind her and without moving began to explain that he was “just trying to get a rise out of her.” She repeated again, “Please get out of my personal space.” He stated, still without moving, “I don't know, I guess I thought you might hit me or something” and finally wandered off. The female player was visibly shaken by the interaction. The statement that he thought he might get hit seemed to indicate to me that the player knew this was not something he should be doing.
The incident was reported to the LGS staff. This did not happen at a Magic event, it was organized Dungeons and Dragons play through adventure league. I want to do something but I have no idea what to do. Any help would be appreciated.

From the man's behaviour, it looks like he knew that what he was doing would piss off the female player, not just make her uncomfortable like anyone would be if someone did that.

As you said, this was not MtG sanctioned play. But you don't need to be a judge to act in this situation. If you feel like someone is doing something they shouldn't do go ahead and try to make the person stop, go talk to the staff, and if the problem persists go and report the store for allowing this behaviour, they are still bound by the WPN Terms and Conditions, including the WPN Code of Conduct.

You may not have the authority of a judge in that context but you don't need it. What you have is the confidence, the charisma and the players' trust of a judge (this last part assuming there is some overlap between MtG and D&D players at your LGS and this is your LGS).

I also feel like this piece of text from the Judge Code of Conduct is relevant here:

Judges should not allow others to create a bad environment by inaction

One could argue that creating a bad environment at a LGS outside MtG play will damage the image of the LGS and make Magic players leave the store for another place, because they don't feel comfortable here anymore.

Let me be clear, I don't blame you for the course of actions you took, I cannot say I would have acted differently in this situation. Or better, I blame you the same way I would expect anyone to blame me if I had done what you did and with the information you gave us. It doesn't mean you're the only one to blame.

Regarding your future course of action. If you have the occasion to go back to that LGS, go talk to the female player, investigate in order to know if the behaviour you witnessed is a recurrent thing, talk to the staff, ask them about that player, if he is known for doing that, if there was a grief with the female player previously. And the next time this kind of thing happens step up, talk to the man (or bring a staff member to talk to him). As Adventure League is Wizards sponsored there could be play consequences for more than the involved persons, set aside complaints for harassment.

This is a matter well beyond the scope of event rules and Wizards event policy. This is intimidation, harassment, and assault and should be handled as such.

If you are in a position and authority to do so, this is a case where you must ask why you are not acting to protect a patron and why that assailant is not being escorted from the premises.

As a witness, you may at the very least ask the victim if she would like for you to call the police. You may also simply call the police outright as you are witness to a crime.