Meets the standards. In the days of bare-knuckle fighting, bouts took place within a large circle drawn on the bare ground (that's where the phrase “boxing ring” came from). The contest began with the fighters facing off while standing on either side of a line scratched on the dirt in the middle of the ring. A fighter who was physically and mentally ready to take part stood at the line and was, therefore, up to scratch. “Up to snuff ” has much the same meaning. Powdered tobacco was said to sharpen the user's mind, so if you were up to snuff, you were mentally and also physically ready to go.