A second attempt to bring in one off-course (6)
I believe the answer is:
Here is my best explanation:
'off-course' is the definition.
(I've seen this before)
'a second attempt to bring in one' is the subsidiary indication.
'a second' becomes 'as' (I've seen this in other clues**).
'attempt' becomes 'try' ('try' can be a synonym of 'attempt').
'to bring in' indicates putting letters inside.
'one' becomes 'a'.
'try' placed around 'a' is 'tray'.
(Other definitions for astray that I've seen before include "Off the correct path", "Off the mark!", "on the wrong road", "missing?", "Wandering off the path", "wide of the mark", "Off one's route or lost", "Well off course", "Wandering, errant" and "Off the track - in error".)