It looks like you got daytime sports covered. It's the indoor and nighttime that has already been mentioned that is really tricky to get a good shot. When it comes to hobby photographers it's about give and take with what we have, what we can afford, and working with what we got. You already got some great suggestions on some good lens that will do what you want but as you can see will be really $$$.
Bumping your ISO will give you more light which you can use for a faster shutter speed to stop motion. Though, like you already have seen you are going to get some noise (grainy) texture. Depending of what camera you have anything passed 800 ISO is going to start to get grainy.
The lenses you have now aren't the best at indoor/nighttime, the maximum aperture you have is 3.5, which is why you got some decent volleyball ones on your 28-80mm. You should get at least try to find f/2.8 so you can get some more light to come through the lens. So you can take down the ISO to get less noise and still have the fast speed you are looking for in stopping motion. The picture below shows the difference sizes of apertures. The bigger the circle, the more light can be collected by the lens to be processes through the camera. So when it comes to poor lighting (indoor light, nighttime stadiums) the best maximum aperture to get is the f1.4. The only negative about apertures is those 1.4-2.8 can get really pricey, specially with increasing distance.
Now you need to look at what is the necessary distance to get your picture. Indoor volleyball you should be able to get fairly close, but for football/baseball you already know you have to get at least 200-400mm.
I would recommend waiting awhile and save up for the lens suggested like the Sigma 70-200mm f2.8 or something to that range.
I have gotten by with a f4-5.6 70-300mm lens on some nighttime baseball of my cousin. I went to full manual mode and fine tune the adjustments to get some decent shots with throwing/batting action. Granted I was usually in 1600 or even 3200 ISO at times, some photoshop editing cleared it up pretty nicely. Before the game do some testing shots to get what adjustments is needed to get the pictures you want. I will be doing some indoor track pictures soon and lucky to have some old manual f2.8 lenses to get some good shots.
Just keep learning, and good luck finding what you need.