By chance, stress colleague grabbing passport? (12)
I believe the answer is:
accidentally
'by chance' is the definition.
('accidentally' can be a synonym of 'by chance')
'stress colleague grabbing passport?' is the wordplay.
'stress' becomes 'accent' ('accent' can be a synonym of 'stress').
'colleague' becomes 'ally' (I've seen this before).
'grabbing' is an insertion indicator.
'passport?' becomes 'id'.
'accent'+'ally'='accentally'
'accentally' going around 'id' is 'ACCIDENTALLY'.
(Other definitions for accidentally that I've seen before include "Inadvertently, by chance" , "Not purposefully, by mistake" .)