Love Enid's movement in legal position (6)
I believe the answer is:
onside
'in legal position' is the definition.
(in a legal position in eg football)
'love enid's movement' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'movement' indicates anagramming the letters (letters move around).
'enids' with letters rearranged gives 'nside'.
'o'+'nside'='ONSIDE'
(Other definitions for onside that I've seen before include "Legally positioned in game" , "In OK position to achieve goal" , "in position to proceed?" , "In agreement (colloq.)" , "In a legal position (football)" .)