Trusty leaders of local organisation backed nonprofessional (5)
I believe the answer is:
loyal
'trusty' is the definition.
(thesaurus)
'leaders of local organisation backed nonprofessional' is the wordplay.
'leaders of' indicates taking the first letters.
'backed' says the letters should be written in reverse.
'nonprofessional' becomes 'lay' ('lay' can be a synonym of 'nonprofessional').
The first letters of 'local organisation' is 'lo'.
'lay' backwards is 'yal'.
'lo'+'yal'='LOYAL'
(Other definitions for loyal that I've seen before include "Sort of toast" , "Staunch" , "Alloy (anag.)" , "Keeping faith" , "Faithful to country, cause or friend" .)