back somebody up = to support somebody;

back away (intransitive) = to go back slowly

back out (intransitive) = to withdraw from a previous committment.

Prasal verb Translation Examples
back somebody up appoggiare qualcuno We decided to back up their candidate because he had promised to intervene for the solution of our problem.
back away spostarsi all’indietro  As soon as he got out his knife Paul backed away to keep at distance.
back out tirarsi indietro da un impegno assunto  He promised that he would sign our petition but later he backed out because he feared the consequences of that act.