Left old friend casing clubs in the area (7)
I believe the answer is:
locally
'in the area' is the definition.
'left old friend casing clubs' is the wordplay.
'left' becomes 'l' (common abbreviation**).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'friend' becomes 'ally' ('ally' can be a synonym of 'friend').
'casing' is an insertion indicator (I've seen this in other clues).
'clubs' becomes 'c' (abbreviation used in card games such as bridge).
'o'+'ally'='oally'
'oally' placed around 'c' is 'ocally'.
'l'+'ocally'='LOCALLY'
(Other definitions for locally that I've seen before include "Nearby" , "In the immediate neighbourhood" , "Within a particular area" , "Happening in neighbouring district" , "In the surrounding area" .)