Start from scratch
Begin (again) from the beginning, embark on something without any preparation or advantage.
As well as the common meaning of the word 'scratch', that is, 'a slight tearing or incision of the skin', there is another meaning which is used in a string of phrases that include the word. These expressions include 'come up to scratch', 'scratch golfer', 'toe the scratch' (a variant of toe the line), 'make from scratch' and 'start from scratch'. What all of these have in common is the notion of 'scratch' being the beginning - a point at which there is no advantage or disadvantage. This meaning originated in the sporting world, where 'scratch' has been used since the 18th century to describe a starting line that was scratched on the ground.
Boxing, golf, cricket and also any sport that involves some form of race use lines on the ground as part of their regulations and historians of each sport encourage the belief that their 'scratch' was the first. Cricket has the strongest claim. Everyone who ever played cricket as a child will be familiar with the batting and bowling 'creases' and will have scratched them on the ground to mark out the pitch. The first time that such a 'scratch' is referred to in print is in a cricketing manual - John Nyren's Young Cricketer's Tutor, 1833, which records this line from a 1778 work by Cotton:
"Ye strikers... Stand firm to your scratch, let your bat be upright."
The positions of boxers who faced each other at the beginning of a bout used to be marked by a scratched line and boxing has the best claim to have been the source of 'toe the scratch' (toe the line).
The expression 'start from scratch' came about in 'handicap' races where weaker entrants were given a head start. Other sports, notably golf, have taken up the figurative use of 'scratch' to mean 'with no advantage - starting from nothing'. The first person who is recorded as 'starting from scratch' was participating in 'pedestrianism' - what we would now call running. The British sporting newspaper The Era reported on a handicap running event in Sheffield in December 1853:
The match on the Hyde Park Ground, Sheffield... has already created quite a furore of excitement among the sporting men of the North. The manner in which the men have been handicapped [is]: James Pudney (of Mile-end) and James Sherdon (of Sheffield), start from scratch; John Syddall, six yards; Richard Conway, twelve; John Saville, twenty...
I do hope that Hyde Park was in fact the first place where the expression 'start from scratch' was first written down, as it is just a mile or so from where I sit and write this stuff.