Crib rails gape badly around infant's head (10)
I believe the answer is:
plagiarise
'crib' is the definition.
('crib'->'plagiarize' is in my internal thesaurus and 'ize'->'ise')
'rails gape badly around infant's head' is the wordplay.
'badly' is an anagram indicator.
'around' means one lot of letters goes inside another.
'head' suggests taking the first letters.
The first letter of 'infants' is 'i'.
'rails'+'gape'='railsgape'
'railsgape' anagrammed gives 'plagiarse'.
'plagiarse' enclosing 'i' is 'PLAGIARISE'.
(Other definitions for plagiarise that I've seen before include "Cheat by copying; agile pairs (anag.)" , "lift!" , "appropriate" .)