All in all for the shutter time and subject matter you did very well to get a photo as clean as you did.

Here are the causes of the imperfections you notice in your photo:

• The people in the photo are moving too fast for the shutter time of 1/80 second. Don't be afraid to push the ISO up to 400 or even 800 so that you can use a shutter time of 1/320 or 1/640 second to freeze moving/jumping people.
• At f/1.8 your lens will be less sharp than stopped down a couple of clicks. This is true of the vast majority of lenses. Use some of that speed you gain by raising the ISO to 800 and set the aperture at f/2.2 or f/2.5 and adjust the shutter time to 1/400 or 1/320 second.
• With such a wide aperture the depth of field will be fairly shallow, so the people in the background will not be as sharp as the person you are focused on. Closing the aperture a little will help some, but there's always only one distance that will be in sharpest focus. That's OK, though, as it looks natural to most viewers and helps guide the viewer's eye to the primary subject that would otherwise be lost in that sea of people.

I shoot similar photos in the gym at a local high school at pep rallies. I usually use ISO 2500 or so with f/2.8 on my 70-200mm telephoto lens (it is very good even wide open) and f/4 on my 24-105mm and/or 17-40mm lenses.