Where leg is on insect (7)
I believe the answer is:
cricket
I believe this is a double definition.
'where leg is on' is the first definition.
(leg is part of a cricket pitch also called on)
'insect' is the second definition.
(cricket is a kind of insect)
(Other definitions for cricket that I've seen before include "short leg seen on this field?" , "English game or chirping insect" , "Ball game" , "little creature" , "Game - "basically baseball on Valium" (Robin Williams)" .)