Square one may be a reference to a board game such as Snakes and Ladders or may come from the notional division of a football pitch into eight numbered sections for the purpose of early radio commentaries.
back the wrong horse
Make a wrong or inappropriate choice.
be on someone's back
nag someone – informal
get off someone's back
stop nagging someone – informal
by the back door
using indirect or dishonest means to achieve an objective
get someone's back up
make someone annoyed or angry.
This phrase developed as an allusion to the way a cat arches its back when it is angry or threatened.
get your own back
have your revenge
retaliate - British informal
know something like the back of your hand
be entirely familiar with something.
not in my backyard = nimby
expressing an objection to the sitting of something regarded as undesirable in your own neighborhood, with the implication that it would be acceptable elsewhere.
This expression originated in the USA in derogatory references to anti-nuclear campaigners. In Britain it is particularly associated with reports of the then Environment Secretary Nicholas Ridley's opposition in 1988 to housing developments near his own home. More recently, it has been used in association with the sitting of housing for refugees and asylum seekers. The phrase has given rise to the acronym nimby as a term for someone with these attitudes.
on your back
in bed recovering from an injury or illness
put your back into
approach a task with vigor.
see the back of
be rid of an unwanted person or thing - British informal
someone's back is turned
someone's attention is elsewhere.
1989 - Orson Scott Card - Prentice Alvin – That prentice of yours look strong enough to dig it himself, if he doesn't lazy off and sleep when your back is turned.
take a back seat
take or be given a less important position or role.
Compare with in the driver's seat.
with your back to the wall = with your back up against the wall
in a desperate situation
put backbone into someone
encourage someone to behave resolutely.
As a metaphor for firmness of character, backbone dates from the mid 19th century.
1998 – Spectator - There is a widespread belief that if only Mrs. Thatcher had still been in No. 10, she would have put backbone into Bush and got rid of Saddam.