A number possibly ignore a form of restraint (3,4)
I believe the answer is:
leg iron
'restraint' is the definition.
(I've seen this before)
'a number possibly ignore' is the wordplay.
'a number' becomes 'L' (fifty in Roman numerals).
'possibly' indicates an anagram.
'ignore' with letters rearranged gives 'egiron'.
'l'+'egiron'='LEG-IRON'
'a form of' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for leg iron that I've seen before include "restriction put on pin" , "Fetter" , "which delays flight indefinitely" , "Ankle restraint for a prisoner" .)