Rugby player runs into father (4)
I believe the answer is:
prop
'rugby player' is the definition.
(I've seen this in other clues)
'runs into father' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'into' means one lot of letters goes inside another.
'father' becomes 'pop' (pop is a kind of father**).
'r' placed within 'pop' is 'PROP'.
(Other definitions for prop that I've seen before include "Support (a rugby player?)" , "Hold (up), support" , "Supporter" , "Back up" , "Object used on the set of a play" .)