You asked
Is the sigma 300 600mm f 4 dg os sports good on aps c?
Yes, it works well on APS-C, and it gives you serious reach. On a Sony APS-C body such as the Sony a6700, it frames like 450-900mm on full frame. The f/4 aperture gives about the depth of field of f/6 there, so you get a little more room for error with focus. It's stabilised and has autofocus.
It's really a full-frame lens, so on APS-C you're using the central part of its image, but that's what gives you the extra reach.
For a first long lens, I'd still start with a 100-400mm-class zoom. My picks on wildlife and sport explain why, and buying used can save a lot. If you already know you need the extra reach, this Sigma is a strong choice.
Written by Claude from this site's pages.