As Tony said, blur and focus are usually two different subjects. Blur is where things move too fast or the camera moved during exposure. Focus is the subject of the photo not being sharp.
As Itai wrote about, because you mentioned your dog running, I'm going to start off with your issue being shutter speed.
Coming from just shooting an indoor dog sporting event, I pushed my D7000 to (what I consider to be) its limit for both high ISO and autofocus performance and walked away with about a 30-40 percent success rate.
With trying to keep ISO as low as possible, because of the such poor indoor lighting, I first TRIED to shoot at a shutter speed of 1/320 to 1/500, at f/2.8. This simply isn't fast enough shutter to freeze much movement. At 1/500 I was barely able to freeze the fast moving dogs.
I ended up doing two things before I was able to get my shutter speed up to 1/800 - 1/1000 and started getting non-blurry images that were not underexposed:
- Bump the ISO up to 3200
- Switch from my f/2.8 zooms to an 85mm f/1.8 and shot it wide open
Because of the such shallow depth of field at f/1.8, I still missed focus on some shots, but the parts of the dog that were in focus (e.g. their tail), had very little to no blurring.
Now, onto the issue of focus.
What really helped me here was knowing the different autofocus modes of the D7000. The setting that gave me the best results for the conditions I was in at the time was continuous AF setting and the 3D autofocus mode with the main autofocus point moved 3-4 spots to the right. This let me get initial lock on the dog's head as it moved from my right to left. And, as I was panning the camera, the D7000 automatically moved the focus point to the left, keeping the dog's head in focus.
The explanation of all the autofocus modes in the D7000 manual is pretty much non-existant. To fully understand how all of the autofocus modes function, I highly recommend the following PDF:
Nikon D7000 Autofocus System Explained:
This document goes into great detail about each mode, scenarios when to use them and includes screenshots of the settings.