Trying standard formation initially stops poor results (9)
I believe the answer is:
stressful
'trying' is the definition.
(I know that trying can be written as stressful)
'standard formation initially stops poor results' is the wordplay.
'initially' says to take the initial letters.
'stops' means one lot of letters goes inside another (stopping can mean blocking a gap).
'poor' indicates an anagram.
The first letters of 'standard formation' is 'sf'.
'results' is an anagram of 'stresul'.
'sf' put inside 'stresul' is 'STRESSFUL'.
(Other definitions for stressful that I've seen before include "Causing mental tension" , "Creating tension" , "Worrying" , "tense" , "Very hard on the nerves" .)