Trusty leaders of local organisation backed nonprofessional (5)
I believe the answer is:
Here is my best explanation:
'trusty' is the definition.
'leaders of local organisation backed nonprofessional' is the subsidiary indication.
'leaders of' suggests taking the first letters.
'backed' is a reversal indicator.
'nonprofessional' becomes 'lay' ('lay' can be a synonym of 'nonprofessional').
The first letters of 'local organisation' is 'lo'.
'lay' back-to-front is 'yal'.
(Other definitions for loyal that I've seen before include "Alloy (anag.)", "Trusty", "Steadfast and true", "Unwaveringly devoted to friend or cause", "Trustworthy", "True to one's country etc", "Keeping faith", "True and faithful", "Steadfast in allegiance" and "Devoted".)