Family member is on lawn playing (3-2-3)
I believe the answer is:
son-in-law
'family member' is the definition.
(I've seen this before)
'is on lawn playing' is the wordplay.
'playing' indicates anagramming the letters.
'is'+'on'+'lawn'='isonlawn'
'isonlawn' anagrammed gives 'SON-IN-LAW'.
(Other definitions for son-in-law that I've seen before include "Daughter's husband" , "Member of extended family" , "Relative by marriage" , "He's married to your daughter" .)