from scratch from the very beginning, especially without utilizing or relying on any previous work for assistance.

☞ In certain sports, the scratch was originally the line or mark drawn to indicate the point from which competitors had to start a race unless they had been awarded an advantage and were able to start ahead of this line. So, a competitor starting from scratch would start from a position without any advantage. The expression up to scratch (see below) also comes from this sense of the noun scratch: a competitor who was up to scratch was of a good enough standard to start a race.