Boxer’s dad securing time at last with rowing crew (13)
I believe the answer is:
featherweight
'boxer's' is the definition.
(featherweight is a kind of boxer)
'dad securing time at last with rowing crew' is the wordplay.
'dad' becomes 'father' (I've seen this in another clue).
'securing' indicates putting letters inside.
'at last' says to take the final letters.
'with' becomes 'w' (abbreviation).
'rowing crew' becomes 'eight' (a crew of eight rowers is called an 'eight').
The last letter of 'time' is 'e'.
'father' enclosing 'e' is 'feather'.
'feather'+'w'+'eight'='FEATHERWEIGHT'
(Other definitions for featherweight that I've seen before include "Light and of little importance" , "one might be counted out?" , "Sportsman" , "Light boxer" , "Nobody" .)