Squadron leader tried to break step (6)
I believe the answer is:
stride
'step' is the definition.
(I know that stride is a type of step)
'squadron leader tried to break' is the wordplay.
'leader' indicates taking the first letters.
'to break' is an anagram indicator.
The first letter of 'squadron' is 's'.
'tried' is an anagram of 'tride'.
's'+'tride'='STRIDE'
(Other definitions for stride that I've seen before include "Walk with long steps" , "Take a long step" , "Long pace" , "Take long paces" , "Take long steps" .)