I don't like the Nikon TC myself. I have a good, older one, but any TC has never done it for me. Better off with a good, dedicated lens that goes to 300mm. I suggest avoiding the 70-300mm VR zoom myself. It covers full frame, is very inexpensive, but at around 270mm to 300mm it goes real soft, IMO. Not that fast AF either, at least for me. I use it for birding, but I thik for sports you would find it fustraiting. I have a 35 year old 300mm F4.5 Nikkor, fixed focal lenght and MF, which I find sharper than the 70 to 300mm at 300mm.
for reasonable cost, and good AF speed, look at the Nikon 300mm f4 IF/ED Lens.