Press runner losing the lead (7)
I believe the answer is:
printer
'press' is the definition.
(thesaurus)
'runner losing the lead' is the wordplay.
'runner' becomes 'sprinter' (sprinter is a kind of runner).
'losing the lead' means to remove the first letter (the letter which leads the word is removed).
'sprinter' with its first letter taken away is 'PRINTER'.
(Other definitions for printer that I've seen before include "Producer of reading material" , "See 13 Down" , "who makes an impression" , "Computer peripheral" , "Computer attachment to produce paper documents" .)