I have a D7000 and need a lens to shoot horses performing indoors (low light) moving quite fast. I need a lens can photograph horses, ideally, up to 20 metres away. Excuse my ignorance, I understand horses....not photography.
This lens makes a good portrait lens for close ups. You might want to consider the flexibility of a zoom Nikkor 70-300mm is a good option. I have both lenses and the flexibility to quickly frame by zooming in and out on moving subjects like your talking about, might be better. To frame using this prime lens (fixed focal length) will mean you moving around with the camera. The lens is sharp and performs well in low light although the results are a little soft wide open (f1.8) but once the aperture is reduced to say f2.8 and smaller (a larger f number) the results are quite brilliant. The crop value on your D7000, being a DX camera, is 1.5x meaning this 50mm lens actually becomes a 75mm which is why people say its a good lens for portraits where you can get close to the subject. This may not be the case for the moving horses which is why the flexibility of a zoom might be better for you. Its great value for the money and I bought it for portraits and to use on a full frame FX D800 camera body as a standard lens but for landscapes and not moving subjects. Hope this helps.