hey, I think a lot of these are BrEnglish idioms. For those, I'll provide examples so someone else can better understand the context.
A: Keep moving the goalposts-I think this means to change the approach to a problem?
Ex: "Preschool for All" supporters keep moving the goalposts in the debate over universal preschool, desperately searching for an argument that can actually hold up to scrutiny.
B: A level playing field
Fair competition, where no advantage is shown to either side.
This phrase clearly alludes to the requirement for fairness in games which are played from end to end and where a slope would give one team and advantage, e.g. football. The figurative use of the phrase isn't especially old and the first record I can find of it is from the magazine American Banker, January 1979:
"[He] said the Oregon BA welcomed 'any and all competition, on a level playing field'."
This harks back to another American phrase, from about a century before - on the level. This is first recorded in George Burnham's
Memoirs of the United States Secret Service, 1872:
"On the level, meeting a man with honorable intentions."
C: back the wrong horse
Also, bet on the wrong horse. Guess wrongly or misjudge a future outcome, as in Jones garnered only a few hundred votes; we obviously backed the wrong horse, or Counting on the price of IBM to rise sharply was betting on the wrong horse. Transferred from wagering money on a horse that fails to win the race, a usage dating from the late 1600s, this term is widely applied to elections and other situations of uncertain outcome.
D: par for the course:
An average or normal amount; just what one might expect. For example, I missed three questions, but that's par for the course. This term comes from golf, where it refers to the number of strokes needed by an expert golfer to finish the entire course. Its figurative use for other kinds of expectation dates from the second half of the 1900s.
E: hourses for courses:
something that you say which means that it is important to choose suitable people for particular activities because everyone has different skills. Ah well, horses for courses. Just because a plumber can mend your washing machine, it doesn't follow that he can mend your car as well.
F: touch base
to talk to someone in order to find out how they are or what they think about something. I had a really good time in Paris. I touched base with some old friends and made a few new ones. (usually + with)
G: neck and neck:
very close or equal. The two companies are neck and neck in the competition to win over customers.
Usage notes: generally used to describe competitors, and often with the verb run: The two candidates are running neck and neck in the opinion polls.
Etymology: based on the meaning in horse racing of horse running neck and neck (= at the same speed with their heads and necks next to each other)
H: a major player: be well-known?
I: keep (people) on side:??
Any questions, don't hesitate to ask.