Left Old Boy, shy (3)
I believe the answer is:
lob
'shy' is the definition.
(I've seen this in other clues)
'left old boy' is the wordplay.
'left' becomes 'l' (common abbreviation).
'old boy' becomes 'OB' (abbreviation for a private school 'old boy').
'l'+'ob'='LOB'
(Other definitions for lob that I've seen before include "Tennis shot" , "Propel in a high arc" , "High shot" , "Toss" , "Lofted ball" .)