Frog leaned to have a look (4)
I believe the answer is:
ogle
'a look' is the definition.
(I know that ogle is a more specific form of look)
'frog leaned to have' is the wordplay.
'to have' indicates the answer is hidden within the clue.
'OGLE' is hidden in the letters of 'frog leaned'.
(Other definitions for ogle that I've seen before include "Look flirtatiously at" , "Close scrutiny" , "Gaze at lecherously" , "lewd look" , "Stare at lecherously" .)