Caught with speed ? it's pure (6)
I believe the answer is:
chaste
'pure' is the definition.
(chaste means abstaining from sex)
'caught with speed ?' is the wordplay.
'caught with' becomes 'c' (cricket abbreviation. I am not sure about the 'with' bit.).
'speed ?' becomes 'haste' (haste is a kind of speed ).
'c'+'haste'='CHASTE'
'it's' is the link.
(Other definitions for chaste that I've seen before include "Like Diana" , "He-cats could be virtuous, strangely" , "Maidenly" , "Morally pure" , "Undefiled" .)