Dogs move so fast that you’re going to need a high shutter speed, which implies a relatively wide aperture and high ISO, which implies short DOF, etc. There are no other choices unless the photographer is doing some kind of stylized shooting with blurred images. Since dogs tend to play on open ground, like school yards or park land, there is little choice except a low angle perspective. As for head-on, well, that’s one of two options: The other is side shots. When I shot dogs playing, I’ll take anything I can get, head-on or side shots — they’re equally illustrative of how dogs play.