Well, it isn't what I've been asking Sigma for, but it'll work for outdoor field sports, at least during daytime. The question is: will it deliver excellent images, corner to corner, wide open, over its entire zoom range? When I say excellent, I mean as good as my 300 f/2.8 with or without 1.4x or 2x TC.
Uh, no. If it did, it would cost a heck of a lot more than 2000.
I imagine it will be marginally better than the tamron, but it isn't going to out do or match a prime across a 4X zoom range.